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Statistical analysis and modeling of breast cancer and lung cancer
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Dissertation (PHD)University of South Florida, 2010.
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ABSTRACT: The objective of the present study is to investigate various problems associate with breast cancer and lung cancer patients. In this study, we compare the effectiveness of breast cancer treatments using decision tree analysis and come to the conclusion that although certain treatment shows overall effectiveness over the others, physicians or doctors should discretionally give different treatment to breast cancer patients based on their characteristics. Reoccurrence time of breast caner patients who receive different treatments are compared in an overall sense, histology type is also taken into consideration. To further understand the relation between relapse time and other variables, statistical models are applied to identify the attribute variables and predict the relapse time. Of equal importance, the transition between different breast cancer stages are analyzed through Markov Chain which not only gives the transition probability between stages for specific treatment but also provide guidance on breast cancer treatment based on stating information. Sensitivity analysis is conducted on breast cancer doubling time which involves two commonly used assumptions: spherical tumor and exponential growth of tumor and the analysis reveals that variation from those assumptions could cause very different statistical behavior of breast cancer doubling time. In lung cancer study, we investigate the mortality time of lung cancer patients from several different perspectives: gender, cigarettes per day and duration of smoking. Statistical model is also used to predict the mortality time of lung cancer patients.
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Advisor: Christos Tsokos, Ph.D.
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Decision tree
Survival analysis
Accelerated failure model
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x Mathematics and Statistics
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Statistical Analysis and Modeling of Breast Cancer and Lung Cancer by Chunling Cong A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Mathematics and Statistics College of Arts and Sciences University of South Florida Major Professor: Chris Tsokos, Ph.D. Gangaram Ladde, Ph.D. Kandethody M. Ramachandran, Ph.D. Wonkuk Kim, Ph.D. Marcus McWaters, Ph.D. Date of Approval: November 5, 2010 Keywords: decision tree, survival analysis, accelerated failure model, Cox proportional hazard model, KaplanMeier Copyright 2010, Chunling Cong
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Dedication I would like to dedicate my dissertati on to my parents, Weihua Cong and Lanzi Peng and my sister Lian Cong for their unconditional support and trust in me which enables me to be confident in myself. I would also like to dedicate my dissertat ion to my advisor Dr. Chris Tsokos. In the past three years, hi s continuous support and encouragement inspired me to never giving up the dream of becoming not only a good statistician, but also a better person. He has also given me lots of opportunities to achieve whatever goal I may have. I have been truly enjoying the wonderful mentor ing relationship with him. He made the whole Ph.D. process a journey full of en deavors, learning experience and feeling of accomplishments.
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Acknowledgements First of all, I would like to thank my dissertation committee for their great efforts in refining my research design and writing. Dr. Chris Tsokos has been given my help and suggestions throughout the whole proc ess and my growing interest in research to a good extent owes to the helpful inputs from Dr. Wonkuk Kim. Dr. Gangaram Ladde has been always very kind and supportive in ev ery step of the way. Dr. Kandethody M. Ramachandran certai nly also contributed a lot to my pleasant and rewarding dissertation process. I am truly grateful for the internship op portunity from American Cancer Society and valuable inputs provided by Dr. James Kepner which makes the current research applicable to real world problems At last, I would like to extend my appreciation to all the memb ers in the cancer research team, their hard work and cooperation made my statistical analysis possible.
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Table of Contents List of Tables iii List of Figures v Abstract vii Chapter 1 Introduction 1 1.1 Breast Cancer and Lung Cancer 1 1.1.1 Breast Cancer 1 1.1.2 Lung Cancer 2 1.2 Decision Tree 3 1.2.1 Introduction to Decision Tree 4 1.2.2 Theory behind Decision Tree Analysis 5 1.2.3 Survival Tree and Random Forest 9 1.3 Survival Analysis 11 1.3.1 Kaplan Meier Estimator 13 1.3.2 Accelerated Failure Time Model 14 1.3.3 Cox Proportion al Hazard Model 15 Chapter 2 Breast Cancer Treatment Effectiveness 17 2.1 Background and Data 17 2.2 Nonparametric Comparison of Treatment Effectiveness 19 2.3 Parametric Comparison of Treatment Effectiveness 21 2.4 Decision Tree Analysis 26 2.5 Conclusion 30 Chapter 3 Statistical Modeling of Breast Cancer Relapse Time 32 3.1 Background and Data 32 3.2 AFT and Cox PH Model 33 3.3 Kaplan Meier VS. Parametric Survival Analysis 37 3.4 Cure Rate Statistical Model 44 3.4.1 Model Introduction 44 3.4.2 Model Results for the Breast Cancer Data 46 3.4.3 Conclusion 49 i
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Chapter 4 Markov Modeling of Breast Cancer Stages 50 4.1 Background 50 4.2 Markov Model 51 4.3 Breast Cancer Markov Chain Model Results 54 4.4 Conclusion 61 Chapter 5 Statistical Comparison between Different Histology Types 62 5.1 Background and Data 62 5.2 Comparison of Survival Time and Relapse Time 64 5.3 Treatment Effectiveness of Different Histology Types 66 5.4 Conclusion 69 Chapter 6 Sensitivity Analysis of Breast Cancer Doubling Time 71 6.1 Background 71 6.2 Breast Cancer Doubling Time Data 74 6.3 Geometrical Formulas of Tumor Volume 77 6.4 Analytical Calculation of Doubling Time 83 6.5 Probability Distributi on of Doubling Time 91 6.6 Conclusion 99 Chapter 7 Statistical Modeling of Lung Cancer Mortality Time 102 7.1 Background and Data 102 7.2 Results of Parametric Analysis 104 7.3 Results of Nonparam etric Comparison 108 7.4 Results of Modeling of Mortality Time 110 7.5 Discussion 117 Chapter 8 Conclusions and Future Research 119 7.1 Conclusions 119 7.2 Future Research 120 References 123 Appendices 126 Appendix A1: Probability Densit y Functions of Distributions 126 About the Author End Page ii
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List of Tables Table 2.1 Test the Difference of Means of Two Treatments 21 Table 2.2 Estimators and Loglik elihood of Lognormal distribution 22 Table 3.1 Factors in Parametric Regression Models for RT+Tam 34 Table 3.2 Factors in Parametr ic Regression Models for Tam 35 Table 3.3 Reoccurrencefree Probability 43 Table 3.4 Cure Rate of Uncured Patients 46 Table 3.5 Cure Rate with Interactions of Uncured Patients 48 Table 4.1 Transition Intensity Matrix of RT+Tam 55 Table 4.2 Transition Intensity Matrix of Tam 55 Table 4.3 2year Transiti on Probability for RT+Tam 58 Table 4.4 2year Transiti on Probability for RT+Tam 59 Table 4.5 4year Transiti on Probability for RT+Tam 59 Table 4.6 4year Transiti on Probability for RT+Tam 59 Table 4.7 5year Transiti on Probability for RT+Tam 59 Table 4.8 5year Transiti on Probability for RT+Tam 60 Table 4.9 10year Transiti on Probability for RT+Tam 60 Table 4.10 10year Transition Probability for RT+Tam 60 Table 5.1 LogRank Test for Survival Time and Relapse Time 69 Table 6.1 Date and Dimensions of Tumor Observations 75 iii
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Table 6.2 Doubling T ime under Linear Growth 86 Table 6.3 Doubling Time under Quadratic Growth 88 Table 6.4 Doubling Time under Exponential Growth 89 Table 6.5 Distribution of Doub ling Time under Linear Growth 93 Table 6.6 Distribution of Doublin g Time under Quadratic Growth 95 Table 6.7 Distribution of Doubling Time under Exponential Growth 98 Table 6.8 Summary of Results 100 Table 7.1 Mean and Standard Deviat ion of Fitted Distribution 106 Table 7.2 Confidence Interv al of Fitted Distribution 107 Table 7.3 Wilcoxin TwoSample Test Result 108 iv
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List of Figures Figure 1.1 CART 6 Figure 1.2 ID3 6 Figure 2.1 Patient Treatment Data 18 Figure 2.2 Survival Curves of Two Treatment Groups 20 Figure 2.3 Fitted Lognormal CDF curve for RT+Tam 23 Figure 2.4 Fitted Lognormal Survival Curve for Tam 24 Figure 2.5 Radiation +Tamoxifen 28 Figure 2.6 Tamoxifen 28 Figure 2.7 Survival Curves for Different Subgroups 29 Figure 3.1 Lognormal VS. KaplanMeier for RT+Tam 38 Figure 3.2 Exponential VS. KaplanMeier for RT+Tam 38 Figure 3.3 Weibull VS. KaplanMeier for RT+Tam 39 Figure 3.4 CoxPH VS. KaplanMeier for RT+Tam 40 Figure 3.5 Lognormal VS. KaplanMeier for Tam 41 Figure 3.6 Exponential VS. KaplanMeier for Tam 41 Figure 3.7 Weibull VS. KaplanMeier for Tam 42 Figure 3.8 CoxPH VS. KaplanMeier for Tam 42 Figure 4.1 Three Stages of Breast Cancer 51 Figure 4.2 Survival Curves of Patients in RT+Tam 57 v
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Figure 4.3 Survival Curve of Patients in Tam 57 Figure 5.1 Breast Cancer Patients by Histology Types and Treatments 63 Figure 5.2 KaplanMeier Curves of Survival Time in DUC and MIX 65 Figure 5.3 KaplanMeier Curves of Relapse Time in DUC and MIX 66 Figure 5.4 KaplanMeier Curves of Survival Time in RT+TAM and TAM 67 Figure 5.5 KaplanMeier Curves of Relapse Time in RT+TAM and TAM 68 Figure 6.1 Breast Cancer Mammogram Data 75 Figure 6.2 Averaged Tumor Size VS. Age 79 Figure 6.3 Average Tumor Size with Age 1748 80 Figure 6.4 Average Tumor Size with Age 4978 81 Figure 6.5 Average Tumor Size with Age above 78 83 Figure 7.1 Lung Cancer Data 103 Figure 7.2 Percentage Plot of Female ExSmokers 113 Figure 7.3 Predicted Survival Curve of Female Smokers 114 Figure 7.4 Percentage Plot of Male ExSmokers 115 Figure 7.5 Predicted Survival Curve of Male Smokers 116 Figure 8.1 Stepwise Vari able Selection Macro 121 vi
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Abstract The objective of the present study is to investigate various problems associate with breast cancer and lung cancer pati ents. In this study, we compare the effectiveness of breast cancer treatment s using decision tree analysis and come to the conclusion that although certain treatment shows overall effectiveness over the others, physicians or doctors should discretionally give different treatment to breast cancer patients based on their characteristics. Reoccurrence time of breast caner patients who receiv e different treatment s are compared in an overall sense, histology type is also taken into consideration. To further understand the relation between relapse time and other variables, statistical models are applied to identify the attribute variables and predict the relapse time. Of equal importance, the transition between different breast cancer stages are analyzed through Markov Chain which not only gives the transition probability between stages for specific treatment but also provide guidance on breast cancer treatment based on stating information. Sensitivity analysis is conducted on breas t cancer doubling time which involves two commonly used assumptions: spheric al tumor and exponential growth of vii
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viii tumor and the analysis reveals that vari ation from those assumptions could cause very different statistical behavior of breast cancer doubling time. In lung cancer study, we investigate the mortality time of lung cancer patients from several different perspectives: gender, cigarettes per day and duration of smoking. Statistical model is also used to predict the mortality time of lung cancer patients.
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Chapter 1 Introduction 1.1 Breast Cancer an d Lung Cancer Cancer is a class of diseases when a cell or group of cells display uncontrolled growth, invasion and sometimes spread to other locations in the body via lymph or blood (metastasis). It causes about 13% of all human deaths in 2007 with a total of 7.6 million affecting people at all ages. Although there are many causes of cancer, 9095% of cancer is caused due to lifestyle and environmental factors and 510% are due to genetics. 1.1.1 Breast cancer According to an authoritative source of information on cancer incidence and survival in the United States: the Surv eillance, Epidemiology and End Results (SEER) Program of the National Cancer Institute (NCI) collects and publishes cancer incidence and survival informati on from around 28 percent of the US population, it is estimat ed that 207,090 women will be diagnosed with and 39,840 women will die of cancer of breast in year 2010. From the statistics based on 2003 to 2007, the median age at diagnosis fo r cancer of the breast was 61 years old, and the incidence rate was 122.9 per 100,000 women per y ear. From the 1
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same data source, the median age at deat h for breast cancer was 68 years old with a death rate of 24. 0 per 100,000 women per year The overall 5year survival for 19992006 was as high as 89.0%. Based on rates from 20052007, 12.15% of women bor n today wi ll be diagnosed with cancer of the breast at some time during their lifetime. In other word s, 1 in 8 women will be diagnosed with breast cancer during their lifetime. 1.1.2 Lung Cancer For lung cancer, it is estimated that 222,520 men and women will be diagnosed with and 157,300 men and women will die of lung and bronc hus cancer in 2010. Based on NCIs SEER Cancer Statistics Re ivew, the incidence rate was 62.5 per 100,000 men and women per year and the median age at death for lung and bronchus cancer was 72 years old, bas ed on the cases diagnosed in 20032007 from 17 SEER geographic areas. The death rate was 52.5 per 100,000 men and women per year. Overall 5year survival rate was 15.8% based on data from 19992006 with highest survival rate 18. 6% for white women and lowest rate 11.3% for black men. As to the lifeti me risk, 6.95% men and women born today will be diagnosed with lung and bronchus cancer at some point during their lifetime. In other words, 1 in 14 men and women will be diagnosed with lung or bronchus cancer durin g their lifetime. Of all cancer incidences among wom en, breast cancer comprises 10.4% worldwide and it is the most common ty pe of nonskin cancer in women and the fifth most common cause of cancer deat h. The primary epidemiologic and risk 2
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factors identified are sex, age, lack of childbearing or breastfeeding, higher hormones level, race and economic status. The most common cause of cancerrela ted death in men and women is lung cancer, responsible for 1.3 million deaths worldwide annually. It is a disease of uncontrolled cell growth in tissues in lung. Due to the high incidence rate and death rate cause by breast cancer and lung cancer, significant amount of statisti cal analysis has been done on causes of cancer, treatment effectiveness, transit ion between cancer stages, prediction of reoccurrence time and survival time. 1.2 Decision tree Recently, the decision tree analysis plays a very significant role in the analysis and modeling of various types of medical dat a, especially in cancer research. In addition, decision tree analysis has been extensively used in areas in the financial world, for example, loan approv al, portfolio management, health & risk assessment, insurance claim evaluation, supply chain management, etc. It is also widely applied in fields such as engineering, forensic examination and biotechnology. The objective of present study is to review the theory behind decision tree analysis and to illustrate its usefulness by applying the subject area to various applications. Furthermore, stat istical software information is given to assist scientists in applying decision tree analysis. 3
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1.2.1 Introduction to Decision Tree A decision tree as a visual a nd analytical decision suppor t tool is a hierarchical tree structure. Inductive machine lear ning algorithms are used to learn the decision function stored in the data of the form 123(,)(,,...,)k X YXXXXY that maps some sets of attributes 123(,,...,)k X XXXY to the conclusion about some target variable Y, and then the target vari able Y can be classified or predicted as necessary. The attributes could be any type of variables and based on the type of the outcomes that we are interested in, a decision tree can be called classification tree in descriptive manner if the outcome is discrete or regression tree in a predictive manner if there are continuous outcomes. The theory of a decision tree has the fo llowing main parts: a root node is the starting point of the tree; branches connect nodes showing the flow from question to answer. Nodes that have child nodes are called interior nodes. leaf or terminal nodes are nodes that do not have child nodes and represent a possible value of target variable given the variables represented by the path from the root. The following graphs are two examples of decision trees of 320 breast cancer patients who received the medical treatme nt of tamoxifen and radiation and 321 patients who received tamoxifen alone respectively. The target variable is relapse time, and the attributes are age, hgb, hist, nodediss, hrlevel, pathsize (will be explained in detail in section 3) As can be seen Figure 1.1 and 1.2, not all attributes are used to split th e nodes. The next section explains the 4
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mathematical algorithms of how to cons truct a decision tree including how an attribute and the value of attribute are chosen to split a given node. There are several advantages of decision tree over other classification theory tools that make decision tree popular besi des its simplicity and interpretability. The approach is supervised le arning that given a traini ng data that consist of input and output, we can induce a decision tree even with little hard data; it performs well with large data in a short ti me, and other statistica l or mathematical techniques can be easily incorporated in it. 1.2.2 Theory behind Decision Tree Analysis The basic idea of decision tree analysis is to spit the given source data set into subsets by recursive portioning of the parent node into child nodes based on the homogeneity of withinnode instances or s eparation of betweennode instances with respect to target variables. For eac h node, attributes are examined and the splitter is chosen to be the attribute such that after dividing the nodes into two child nodes according to the value of the attribute variable, the target variable is differentiated to the best using algorithm Because of this, we need to be able to distinguish between important attributes, and attributes which contribute little to overall decision process. This proc ess is repeated on each child node in a recursive manner until splitting is either n onfeasible or all ce rtain prespecified stopping rules are satisfied. 5
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Class ification & Regression Tree is a decision tree algorithm (L. Breiman, 1984) is a nonparametric probabilit y distribution free technique to construct binary classification or regression trees as shown in Figure 2.1. Splitting points attribute variables and values of chosen variables are chosen based on Gini impurity and Gini gain are given by: 2 1()1(,)(,)(,)m iiiitftiftiftj (,)()()()LLRRistitPitPit LP () itYES: p NO: n RP Figure 1.1. CART Figure 1.2 ID.3 where(,) f tiis the probability of getting i in node and the target variable takes values in {1,2,3m}. is the proportion of cases in node t divided to the left child node and is the proportion of cases in t s ent to the right child node. If the target vari able is continuous, the split cr iterion is used with the Least Squares Deviation (LSD) as impurity measure. If there is no Gini gain or the preset stopping rule are satisfied, the splitting process stops. tLPLP ()Lit ()RitYES: 1 p NO: 1nYES: i p NO: inYES: N p NO: Nn 6
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CHAID (ChiSquared Automatic Interaction Detection) classification technique introduced by Kass (1980) for nominal predictors and extended by Magidson (1993) to ordinal predictors is another effective approach for nominal or ordinal target variable. CHAID exhausts all possi ble pairs of categories of the target variable and merge each pair until there is no statistically significant difference within the pair using Chisquare test. ID.3 (Iterative Dichotomi ser 3) developed by Ross Quinlan (1986) is a classification tree used the concept of information entropy first brought in a publication by Claude Shannon and Warren Weaver (1949) This provides a method to measure the number of bits each attribute can provide, and the attribute that yields the most info rmation gain becomes the most important attribute and it should go at the top of the tree. Repeat this procedure until all instances in the node are in the same category. As shown in Figure 2.2, It works in t he following manner. S uppose there are only two outcomes Yes and No in the root node T of target variable. Let p and n denotes the number of posit ive records and negative re cords, respectively. The initial information entropy is given by: 22(,)log log p pnn Ipn p npnpnp n If attribute X with values { , } is chosen to be the split predictor and partition the initial node into { , }, and 1x2x1TNx T2TNi p and denotes the number of in 7
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positive records and negative records in the child node i. Then the expected information() E IXand information gain are given by, () GX 1 iipn pn )()()N ii iEI X Ipn, Information gain GX. ()(,)( IpnEIX In 1993, Ross Quinlan made several improv ements to ID.3 and extended it to C4.5 Unlike ID.3 which deals with discr ete attributes, C4.5 handles both continuous and discrete attributes by creating a threshold to split the attribute into two groups, those above the threshold and those that are up to and including the threshold. C4.5 also deals with records that have unknown attribute values. C4.5 algorithm used normalized information gain or gain ratio as a modified splitting criterion of information gain which is the ratio of information gain divided by the information due to the split of a node on t he basis of the value of a specific attribute. The reason of th is modification is that the information gain tends to favor attributes that have a large number of values. The best approach in selecting the attribut e for a specific node is to choose the one that maximize the given ratio. St opping rule of C4.5 needs to be prespecified and it initiated a pruning procedures by replac ing branches that do not help with leaf nodes after t hey are created to decrease overall tree size and the estimated error of the tree. A rule se t can be derived from the decision tree constructed by writing a rule for each pat h from the root node to the leaf node. After C4.5, Quinlan created C5.0 as an extended commercial version of C4.5 8
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featuring a number of impr ovements including smaller decision trees, weighting different attributes and misclassification types, reducing noise, speed and memory efficiency, support for boosting wh ich gives the trees more accuracy. As a binarysplit algorithm, like CART QUEST (Quick, Unbiased, Efficient, Statistical Tee) proposed by Loh and Shih in 1997 is a classification algorithm dealing with either categorical or continuous predictor X. Pearsons chisquare test is applied to target variable Y and predictor Xs independence if X is a categorical predictor. Otherwis e, if X is continuous, ANO VA F test is performed to test if all the difference classes of Y hav e the same mean of X. In both cases, pvalues are calculated and compared to a Bonferroni adjusted threshold to determine if further Levenes Fstatistics test needs to be performed to determine if the predictor should be chosen as the split predictor for the node. Overfitting occurs in large tree models wh ere the model fits noise in the data, such as including some attributes that are irrelevant to the decisionmaking process. If such a model is applied to data other than the training set, the model may not perform well. There are generally two ways to reduce overfitting: stop growing when data is split not statistically significant, or grow full tree, and then post prune. For example, if Gain of the best attribute at a node is below a threshold, stop and make this node a leaf rather than generating children nodes. 9
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1.2.3 Survival Tree and Random Forest A decision tree is of great importance in classificati on and modeling of healthrelated data and in many situations the data is censored due to various reasons one of which is that some patients left bef ore the end of the per iod of study. Due to the incompleteness of the data, a special portioning and pruning algorithm should be used to construct a survival tree. Gordon and Olshen (1985) gave the first adaption of CART algorithm in cens ored data using Wasserstein metrics to measure distances between KaplanMeier curves and certain point masses After that, Segal (1988) extended regressiontree methodology to rightcensored target variables by replacing the sp litting rules with betweennode separation rules based on the TaroneWare or Harri ngtonFleming classes of twosample statistics and a new pruning algorithm was also devi sed, and truncation and timedependent covariates were included in the method proposed by Bacchetti and Segal (1995). Davis and An derson (1989) used likelihoodratio test to split nodes under parametric exponential distri bution or withinnode constant hazard assumptions. LeBlanc and Crowley used ma rtingale residuals for splitting rule assuming a proportional hazards model and also developed an corresponding efficient pruning algorithm, and the m odel was extended to timedependent case assuming the survival times are piec ewise exponential by Huang, Chen and Soong (1998). Both Davis and Leblanc al gorithms are based on a definition of a withinnode homogeneity measure, unlike Segals algorithm which tried to maximize betweennode separation. Su and Fan extended the CART algorithm to multivariate survival data by introduc ing a gamma distributed frailty to account 10
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for the dependence among survival times based on likelihood ratio test as the splitting function. In addition, this method was extended to competing risks based on proportional hazards for subdistribution of competing risks and deviance was used to grow a tree proposed by Ibrahim, Kudus, Daud and Bakar Random forest is an ensemble classifier first developed by Leo Breiman and Adele Cutler in 2001. Random forest has more accuracy than the singletree model, and handles a very lar ge number of input variables. Besides, it provides a experimental way to detect variable inte ractions, etc. Instead of using all training data, a random sample of N observations with replacement is chosen to build a tree. In the tree building pr ocess, for each node, a random subset of the predictor variables is considered as possible spli tters for each node, a predictor excluded from one split is allowed to be used as splitters in the same tree. Repeat the above procedure until a large num ber of trees are constructed. The average of the predicted value in regr ession trees are computed as the predicted value and the most frequently predicted category in the classifica tion trees are considered to be the predicted category. 1.3 Survival Analysis Survival analysis is widely used in areas that deal with biological organism and failure of mechanical systems. It is a branch of statistical analysis that are commonly seen in engineering, economics or sociology when modeling time to event data, such as death of a cancer patient, failure of a equipment. The difference of survival analysis is that it deals with censoring. Censoring is a form 11
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of missing data problem which is comm on seen in those above mentioned areas. If it is known only that the time of an even t is after some date, it is called right censoring. This often happens when the individual are lo st to follow up or when the study ends after a certain period. Similarl y, if the time of event is know to be less than a certain time; the data is called left censoring. The object of primary interest is to investigate the time of ev ent or the probability of the occurrence of an event after certain time, which is also called a survival probability. Timetoevent data are increasingly common in health research, particularly in longitudinal or cohort studi es where the onset of ce rtain health outcomes is observed. The timing of event onset, in addition to the outcome event (e.g. cure of disease, development of a symptom, death), provides important information about disease progression or treatment effects. Furthermore, the outcome may not be observed on every study subject because of limitations in the study design. For example, a study may terminate before a subject develops the symptom of interest. This characteristic of incomplete observation is called censoring, must be considered in evaluating the study. A survival function measur es the probability of nonevent after certain time which defined as )Pr()(tTtS where is some time, and t T is a random variable denot ing the time of an event. According to definition, a survival func tion is always between 0 and 1. It must be nonincreasing and approac hes 0 as time goes to infinitely. 12
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The corresponding lifetime distribut ion function is defined as )(1)Pr()( tStTtF The hazard function is defined as the event ra te at time t conditional on survival until time t or later. )( )(' )( )( ) Pr()(tS dttS tS dttf tTdttTtdtt. 1.3.1 Kaplan Meier Estimator Nonparametric analysis is used to analyze data without assuming an underlying distribution which avoids potentially larges errors brought about by making incorrect assumptions about the underlying distribution. However, nonparametric analysis usually generated much wider c onfidence bounds than those calculated via parametric analysis and predictions outsi de the range of obs ervations are not possible. Kaplan Meier (KM) estimator, also called product limit estimator is commonly used to get the survival function of lifetime data. A plot of Kaplan Meier estimate of the survival function is a series steps of declining magnitude. When the sample size is large enough wit h respect to the population, KaplanMeier estimator approaches the true surv ival function for the population. Let be the probability that an individual will not have reoccurrence of an event after time t. For a sample of size denote the observed times until death )(tSn 13
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of sample members as nntttt ...321. Then the nonparametric KaplanMeier estimator of the surviv al function is estimated by: i i i ttn nits)(^d KaplanMeier estimator (also known as the product limit estimator) estimates the survival function from survival related dat a. In many medical researches, it is used to measure the portion of patients living for a certai n amount of time after treatment. KaplanMeier is useful when we have censored data, and it is equivalent to the empirical distribution when no truncation or censoring occurs. 1.3.2 Accelerated Fa ilure Time model When covariates are considered, we assume that the relapse time has an explicit relationship with the covariates. Furt hermore, when a parametric model is considered, we assume that the rel apse time follows a given theoretical probability distribution and has an explicit relationship with the covariates. Let denote a continuous nonnegative ran dom variable representing the survival time (relapse time in this ca se), with probability density function (pdf) T f () t () Ft and cumulative distribution (cdf) Pr() Tt We will focus on the survival function the probability of being alive at t (reoccurrence free in this case. In this model we start from a random variable Wwith a standard distribution in and generate a family of survival distributions by introducing location and scale parameters to relate to the relapse time as follows: ()Pr( St (,) Tt ) 14
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logTYW (1) where and are the location and scale parameters, respectively. Adding covariates into the location parameter in equation (1) we have 'logYTx W where the error term Whas a suitable probability distribution, e.g. extreme value, normal or logistic. This transformation l eads to the Weibull, lognormal and loglogistic models forT. This type of statistical models are also called accelerated failure time (AFT) model. 1.3.3 Cox Proportional Hazard Model An alternative approach to modeling surviv al data is to Cox Proportional Hazard (Cox PH) model which assumes that the e ffect of the covariates is to increase or decrease the hazard function by a pr oportionate amount at all durations. Thus, '0(,)() x txte or 0(,) ln () tx x t 15
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where 0() t is the baseline hazard function or the hazard for an individual with covariate values 0, and x e is the relative risk associated with the covariate values x Subsequently, for the survival functions '0(,)()xeStxSt Hence the survival function for covariates x is the baseline survivor raised to a power. Parameter estimates in the CoxPH model are obtained by maximizing the partial likelihood as opposed to the likelihood. The partial likelihood is given by ' uncensoredexp() () exp()i jii Y YYjx L x The log partial likelihood is given by '' Y uncensored YY ()log() log[exp()]ij iijlLxx In application of t he CoxPH model, we also incl uded the interactions of the attributable variables. 16
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Chapter 2 Parametric and Nonparametric Analysis of Breast Cancer Patients with Decision Tree Analysis 2.1 Background and Data Extensive literature and studies can be found related to whether radiation shows a benefit to breast cancer patients with res pect to relapse time. It is clear that radiation makes a difference in recurr ence for some women. However, the potential side effect of heart damage from breast radiation makes it desirable to avoid radiotherapy unless it is absolutely necessary. Therefore, it is of great importance to identify the patients who c ould potentially benefit from radiation and those who would be put at higher risk for receiving radiation treatment. The aim of the present research is to perform parametric, nonparametric, and decision tree analysis to answer the ab ove question. Our parametric and nonparametric analysis confirms the overall advantage of combined radiation and tamoxifen (RT+Tam) over tamoxifen (Tam ) alone in reducing the probability of relapse; however, after utilizing decision tree analysis in conjunction with survival analysis of relapse time of breast c ancer patients, we have concluded under some conditions, giving both treatments to patients without considering the clinicopathological characteristics could be negatively effective or catastrophic. 17
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Between December 1992 and June 2000, a to tal of 769 women were enrolled and randomized, of which 386 received combined radiation and tamoxifen (RT+Tam), and the rest, 383, received tamoxi fenalone (Tam). The last follow up was conducted in the summer of 2002. Only those 641 patients enrolled at the Princess Margaret Hospital are included: 320 and 321 in RT+Tam and Tam treatment group, respectively. This censored data consists of 77 uncensored observations and 564 censored observations as shown in Figure 2.1. T he censored observations are mostly due to two reasons: (1) the breas t cancer patient emigrated out of the study area; (2) the individual survived (did not experienc e occurrence) past the end of the study period. Due to the fact that nearly 90% of the data are censored observations, we take into consideration two datasets, 77 uncensored dataset, and 641 censored dataset for later analysis. 564 censored Observations 77 uncensored Observations 641 (RT + Tam 320 Tam 321) Figure 2.1 Patient Treatment Data In the original data, three relapse events are recorded: local relapse, a xillary relapse and distant relapse. The original dataset was used to analyze competing 18
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risks (also called multiple causes of death) including relapse, second malignancy, and other causes of death. Since in the present study we are interested in the relapse time regardless of the reoccurr ence type, minimum time of the three types of relapse is chosen for analysis purpose, and the values of censoring indicator variable are adjusted accordingl y. Variables assessed at the time of randomization are: pathsize( size of tu mor in cm) ; hist(Histology: DUC=Ductal, LOB=Lobular, MED= Medullar, MIX=Mix ed, OTH=Other); hrlevel( Hormone receptor level: NEG=Negative, PO S=Positive); hgb(Hemoglobin g/l); nodediss( Whether axillary node dissect ion was done: Y=Yes, N=No); age(Age at diagnosis in years). All these attribut able variables will be used in the modeling of breast cancer in a separ ate study where various stat istical models are used to identify the significant prognostic factors in the relapse of breast cancer, as well as the interactions between the variables and ranking of significant individual attributable variables and interactions. 2.2 Nonparametric Analysis KaplanMeier estimator (also known as the product limit estimator) estimates the survival function from survival related dat a. In many medical researches, it is used to measure the portion of patients living for a certai n amount of time after treatment. KaplanMeier is useful wh en we have censored data, and it is equivalent to the empirical distribution when no truncation or censoring occurs. Let be the probability that an individual will not have reoccurrence of breast cancer after time t. For a sample of size denote the observed times until death )( tSn 19
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of pateints as nntttt ...321, the nonparametric KaplanMeier estimator of the survival function is estimated by: i ii ttn dnit s ( )^ KaplanMeier estimates of the survival curves of relapse time for the two treatment groups are shown in Figure 2.2. Figure 2.2 Survival Curves of Two Treatment Groups KaplanMeier is a nonparametric procedure for estimating the survival curve; however, it is not commonly used to co mpare the true mean effectiveness of the Tam RT+Tam 1.0 0.8 0.6 0.4 0.2 0.0 KaplanMeier survival probability 0 246 8 10 Time since randomization (years) 20
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two treatments. In the pr esent study, we perform ac tual nonparametric analysis utilizing Wilcoxon rank sum test and Peto & Peto modification of the GehanWilcoxon test. We proceed in nonparamet ric direction for comparison purpose with the results obtained us ing parametric analysis. Utilizing the two different nonparametric tests, we found the information in Table 2.1, which shows that the combination of the two tr eatments (RT+Tam) is more effective than using the single treatment (Tam) which is consistent with Figure 2.1. Table 2.1 Test the Difference of Means of Two Treatments ChiSquare Degrees of freedom Pvalue Logrank 9.8 1 0.0017 Peto & Peto modification of the GehanWilcoxon 9.6 1 0.00197 2.3 Parametric Analysis First, censored dataset which consists of 641 patients are analyzed, and the characteristic of the behavior of relapse time in RT+Tam arm is investigated through goodness of fit tests. The best pr obability distribution is the lognormal distribution, with corresponding maximu m likelihood estimator (MLE) of the 21
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following form =5.148, =2.47 (as shown in Table 2.2). A graphical presentation of the cu mulative distribution function (CDF) is shown by Figure 2.3 where KaplanMeier curve and its 95% conf idence band, as well as CDF of the fitted lognormal distribution are plotted. Table 2.2 Estimators and loglik elihood of Lognormal Distribution Loglikelihood Totality 4.101 2.04 367 RT+Tam 5.148 2.47 134.4 Tam 3.491 1.79 227.3 22
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024681 0 0.00.20.40.60.81.0 1. KaplanMeier (nonparametric) 2. Lognormal (parametric) Cumulative survival function 1 2 Time since randomization (years) Figure 2.3 Fitted Lognormal CDF Curve for R T + Tam As can be seen from the abov e graph, lognormal probability distribution seems to be a good fit for the relapse time of breas t cancer patients in RT+Tam, and the survival curve from the lognormal probability distribution with estimated parameters is very close to the KaplanMeier survival curve and it is within the 95% confidence band constructed from KaplanMeier survival curve. 23
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Similarly, we perform a parametric analysis for patients in Tam arm. It has been proven through goodnessoffit test that the subjec t data follows a lognormal distribution as well, with MLE of =3.419, =1.79 (as shown in Table 2.2). Therefore, the final estimated form of the lognormal probability distribution is given in Table 2.2 and a graphical form of the cumulative distribution function is given in Figure 2.4. 024681 0 0.00.20.40.60.81.0 1. KaplanMeier (nonparametric) 2. Lognormal (parametric) Cumulative survival function1 2 Time since randomization (years) Figure 2.4 Fitted lognormal survival curve for Tam 24
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Since relapse time in RT+Tam and Tam arm both follow lognormal probability distribution, the loglikelihood ratio te st can be applied to test hypothesis 0H:1 =2 = vs. : 1H1 2 The loglikelihood ratio test statistic is given by T=2[ l ( )l (1 ,2 )]=10.6 with one degree of freedom, and from the Chisquare distribut ion table, pvalue is between 0.05 and 0.001. Thus there is significant difference between the locations of the two treatm ent groups, which is consis tent with the conclusion using nonparametric tests. While for the uncensored dataset of the 77 breast cancer patients, of which 26 are treated with RT+Tam and 51 with Tam alone, in order to perform goodness of fit test to identify the PDF of the 26 patients, we employ bootstrapping technique to increase the sample size of the RT+Tam arm. Through goodness of fit tests including KolmogorovSmirnov, A ndersonDarling and ChiSquare tests, the best fit for RT+Tam is loglogistic probability distribution while the best for Tam arm is general Pareto probability dist ribution. Considering the difference in probability distributions of the two groups, further anal ysis or tests are not conducted to check the mean difference in relapse time. Since consistent results were obtained using nonparametric and par ametric tests wit h regard to the censored dataset, we only c onsidered the censored dat aset for the subsequent analysis. However, as we will see in the following discussi on, after applying 25
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decision tree analysis to partition the subjec t data as a function of the tumor size, age of patient and haemoglobin, the find ings of the two treatments give contradictory results which could be quite misleading in the treatment of breast cancer patients as the nonparametric and parametric analysis indicates. 2.4 Decision Tree Analysis The clinicopathological characters of breast cancer patient s are heterogeneous. Consequently, the survival times are diffe rent in subgroups of patients. Decision tree analysis is used to homogenize the data by separating the data into different subgroups on the basis of similarity of their response to treatment. The general goal of such applications is to identify prognostic factors that are predictive of survival outcome and time to an event of in terest (relapse time in this study). For example, a treebased decision analysis enabl es the natural identification of prognostic groups among patient s, using information available regarding several clinicopathologic variables. Such groupi ngs are important because patients treated with RT+Tam and Tam present cons iderable heterogene ity in terms of relapse time, and the groupings allow ph ysicians to make early yet prudent decisions regarding adjuvant combination therapies. The concept of exponential decision tree anal ysis [5] is to reduce the impurity within nodes by splitting based on covariates using a specified loss function. Assuming the hazard rate withi n a given node is constant, ()jhy for all y in group j and then the survival functi on within each node is an exponential function. The split point is selected so that the loss among the possible binary 26
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splits defined by the cova riates are minimized. The loss function for a node t is given by )/log( )( )(Tt ttYDDDtLtR Where is the number of complete obs er vations at the node and is the total observed time. t iD iyidt iY Considering our main focus here is to compare the two treatments instead of analyz ing each treatment al one, the maximum tree depth is set to be 3 with complexity parameter 0.02. The trees of RT+Tam and Tam are shown in Figure 2.5 and Figure 2.6 shown below. RT+Tam arm is divided into 4 groups denot ed by RT1,RT2,RT3,RT4 from the left to the right; Tam arm is di vided into 4 groups denoted by T1,T2,T3,T4 from the left to the right. To further investigate the survival curves of a subgroup from different treatment arms, KaplanMeier surv ival curves are plotted in Figure 2.7. Using decision tree analysis we conclude t hat giving radiation to a patient whose tumor size exceeds 3.05cm would be catastrophic as has been shown in Figure 5.3 since patients in RT1 are most likely to relapse. Furthermore, treatment Tam is more effective than treat ment RT+Tam with respect to relapse time has also been shown by the survival curves of T2 and RT2. 27
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321 320 12 28 Figure 2.5 Radiation +Tamoxifen Figure 2.6 Tamoxifen In addition, we can conclude that by using decision tree analysis and the corresponding survival analysis, we can group the breast cancer patients into three clusterings that identify the effectiveness of treatment RT+Tam versus treatment Tam. For example, t he survival curve of RT3 is very close to that of T1, which suggests that for patients whose age is under 74.5 and have tumor size between 1.45cm and 3.05 cm, RT+Tam show s no advantage over Tam. Thus, it would be desirable for this patient not to consider receiving radiation. 308 05.3 size 05.3 size 58 250 5.74 age 5.74 age 131 119 45.1 size 45.1 size 137 184 25.1 144 40 size 25.1 size 5.57 age 5.5785 59 age 5.137 RT1 T1 RT2 hgb 5.137 hgb T4 R T3 RT4 T2 T3
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024681 0 0.40.50.60.70.80.91.0 Time since randomization (years)KaplanMeier survival probability 024681 0 0.40.50.60.70.80.91.0 024681 0 0.40.50.60.70.80.91.0 024681 0 0.40.50.60.70.80.91.0 024681 0 0.40.50.60.70.80.91.0 024681 0 0.40.50.60.70.80.91.0 024681 0 0.40.50.60.70.80.91.0 024681 0 0.40.50.60.70.80.91.0 RT4 T2 RT3 T1 RT2 T3 T4 RT1 Figure 2.7 Survival Curves for Different Subgroups We summarize below when RT+Tam and Tam are almost equally effective (1)RT4, T2, RT3, RT2, T1 (2)T3, T4 (3)RT1 29
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Thus, our findings are important in guiding the physicians to recommend tamoxifen alone without radiation rather than a combined treat ment of tamoxifen and radiation when they are equally effe ctive to breast cancer patients with certain size of tumor, age and hemoglobin level. 2.5 Conclusion The objective of this chapter is to perform parametric, nonparametric, and decision tree analysis to evaluate two tr eatments that are being used for breast cancer patients. Our study is based on util izing real data which was initially used in Tamoxifen with or without breast irradi ation in women of 50 years of age or older with early breast cancer [9], and the data is supplied to us by N.A. Ibrahim Decision tree for competing risks survival probability in breast cancer study [2]. We agree upon certain aspects of our fi ndings with the pub lished results. However, in this manuscript, we focus on relapse time of breast cancer patients instead of survival time and parametri c analysis instead of semiparametric decision tree analysis is app lied to provide more pr ecise recommendations of effectiveness of the two treatments with re spect to reoccurrenc e of breast cancer. Although overall paramet ric and nonparametric compar isons of RT+Tam and Tam arms show that the combination of r adiation and tamoxifen is more effective than tamoxifen alone with regar d to the relapse time of a breast cancer patient, a decision tree analysis for censored data reveals that the heterogeneity of clinicopathological characteristics l ead to important difference between 30
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subgroups of the two treatment groups, thus affecting the decision making process in choosing suitable treatm ent for breast cancer patients. 31
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Chapter 3 Statistical Modeling of Breast Cancer Relapse Time with Different Treatments 3.1 Background and Data In the current chapter, same data is us ed to predict the rel apse time of breast cancer patients with differ ent treatments. The proposed statistical models in the present study are construc ted for patients in RT+Tam Group and Tam group, respectively. Information concerning pote ntial prognostic factors (attributable variables) are pathsize (size of tumor in cm) ; hist(Histology: DUC=Ductal, LOB=Lobular, MED= Medullar, MIX=Mix ed, OTH=Other); hrlevel (Hormone receptor level: NEG=Negative, POS=Po sitive); hgb (Hemoglobin g/l); nodediss (Whether axillary node disse ction was done: Y=Yes, N=No); age (Age of the patient in years). The dependent variable or response variable is the relapse time (in years) of a given patient. One important question that we will address is that which of these attributable variables are significantly contributing to the response variable the relapse time. In addition, identify all possible contributing to relapse time. 32
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3.2 AFT Model and CoxPH Model As mentioned, for censored data, the mo st commonly used methods is survival analysis. To model the relapse time of brea st cancer patients, accelerated failure time model and cox proportional hazard model are applied. Th e major objective of applying these models is to identify wh ich of the six attri butable variables are significant contributing to the relapse time of breast cancer patients receiving different treatments. The six explanatory variables used in the models are pathsize (size of tumor in cm) ; hist (Histology: DUC=Ductal, LOB=Lobular, MED= Medullar, MIX=Mixed, OTH=Other); hrlevel (Hormone receptor level: NEG=Negative, POS=Positive); hgb (Hemogl obin g/l); nodediss (Whether axillary node dissection was done: Y=Yes, N=No); age (Age of the patient in years). The most commonly used AFT models such as exponential, Weibull and lognormal AFT models and CoxPH model are applied. After running the model including all covariates and interact ions between covariates, number of parameters that driv e the attributable variables are reduced using stepwise regression based on Arkariki Informati on Critria (AIC) is a measure of the goodness of fit of an estimated statistical m odel. It is trades off the complexity of an estimated model against how well the model fits the data. It is given by where 2log()2() AIClikelihoodpk p is the number of parameter, and k is the number of parameters in the distribution. Statis tical models with lower AIC are preferred. Table 3.1 given below show s the covariates and interactions in the related statistical models chosen using t he AIC as well as their corresponding p33
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values for the breast cancer patients t hat were treated with both radiation and tamoxifen. indicates the variabl es is statistically significant. Table 3.1 Factors in Parametric Regression Models for RT+Tam RT+Tam lognormal exponential Weibull CoxPH AIC 237.64 234.49 235.97 245.8 age 0.002* 0.008* 0.011* 0.01* pathsize 0.01* 0.0002* 0.0002* 0.00086* nodediss 0.021* 0.009* 0.012* 0.012* hrlevel 0.027* 0.010* 0.008* 0.016* age:nodediss 0.037* 0.022* 0.026* 0.028* nodediss:hrlevel 0.009* 0.0005* 0.0008* 0.00067* pathsize:hrlevel 0. 078 0.060 0.041* 0.099 As can be seen from the table, age, pathsize, nodediss hrlevel, and the interactions between age and nodediss, and interaction between nodediss and hrlevel are significant with respect to re lapse time of breast cancer patients who received radiation and tamoxifen. T he interaction of pathsize and hrlevel proves to be significant only in Weibull AFT model. Table 3.2 given below address the same aspec ts as table 3.1, for breast cancer patients that were treated with tamoxifen only. 34
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Table 3.2 Factors in Parametric Regression Models for Tam Tam lognormal exponential Weibull CoxPH AIC 439.34 439.55 440.76 525.89 age 0.343 0.294 0.287 0.32 hgb 0.037* 0.645 0.630 0.68 pathsize 0.339 0.316 0.300 0.33 nodediss 0.025* 0.017* 0.020* 0.018* hrlevel 0.006* 0.002* 0.003* 0.002* age:pathsize 0.143 0.112 0.106 0.120 age:nodediss 0.038* 0.006* 0.007* 0.0065* hgb:nodediss 0.054 0. 077 0.079 0.075 age:hgb NA 0.131 0.128 0.150 For patients who received tamoxifen on ly, only nodediss, hrlevel as single attributable variables are significant with res pect to relapse time in this group. It is worth noticing that although age itself is not significantly contributing to relapse time, the interaction between age and nodedi ss is significant. hgb is found to be significant only in lognormal AFT model. Comparing the results from the two treatment groups, for each group at significance level of 0.05, the three AFT models give almost the same results. Significant prognostic factors for relaps e time of breast cancer patients who 35
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received combined treatment of radiat ion and tamoxifen are age, pathsize, nodediss, hrlevel, age:nodediss, nodediss: hrlevel which appears statistically significant in all lognormal, exponential an d Weibull regression models. Only in Weibull regression model pathsize: hrleve l shows significant contribution to the model. For patients who are in Tam arm, all three models show nodediss, hrlevel and age:nodediss are significant contributing, only in lo gnormal regression model hgb shows significance. Furthermore, significant prognostic factors identified using CoxPH model confirm our conclusion. There are six significantly contributing variables two of which are interactions for RT+Tam arm and three si gnificantly contributing variables one of which is interaction for Tam arm. Next the predicted survival curves of the three AFT models and CoxPH model for each arm are compared to KaplanMe ier survival curve along with 95% confidence band to determine the best predic ting model for relapse time and the results will be shown and discussed. 36
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3.3 KaplanMeier VS. Parametric Survival Analysis From the above four models, we identified the sign ificant attributable variables and interactions between them that contri butes to the relapse time of breast cancer patients in two different treatm ent groups. To investigate which model gives the best fit of the relapse time of breast cancer patients in those two groups, graphical presentation would be a useful to ol. In this study, KaplanMeier curve as a commonly used nonparametric survival curve and its 95% confidence limits are plotted against the survival curves obtained from the four models discussed above to see which model gives the closest curve to KaplanMeier survival curve. Using the breast cancer data for patient s from RT+Tam arm, the KaplanMeier curves along with its 95% confidence limits against th e lognormal AFT model are plotted in Figure 3.1 below. As can be seen from Figure 3. 1, for the second year, th ird year and around the sixth year the survival curve from lognormal AFT model runs out of the 95% confidence band of KaplanMeier curve. For exponential AFT model, the same graphica l representation is given in Fiugre 3.2 below. Form this graph, the survival curve estimated from the exponential AFT model is off the 95% confidence band from year 1 to year 4, and from year 5 to year 6. 37
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024681 0 0.00.20.40.60.81.0 024681 0 0.00.20.40.60.81.0 Timesurvival probablity 2 1 1. KaplanMeier 2. Lognormal Figure 3.1 Lognormal VS. KaplanMeier for RT+Tam Figure 3.2 Exponential VS. KaplanMeier for RT+Tam 024681 0 0.00.20.40.60.81.0 024681 0 0.00.20.40.60.81.0 Timesurvival probablity 2 1 1. KaplanMeier 2. Expone ntial 38
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Figure 3.3 shows the graph of survival curve obtained from the Weibull AFT model, it deviates from the 95% confi dence band of the KaplanMeier in a similar pattern as the survival curv e of the exponential AFT model. 024681 0 0.00.20.40.60.81.0 024681 0 0.00.20.40.60.81.0 Timesurvival probablity 1. KaplanMeier 2. Weibull 1 2 Figure 3.3 Weibull VS. KaplanMeier for RT+Tam Howev er, in Figure 3.4 which shows the su rvival curve obtained from the CoxPH model, it is clear that most of the ti me, the survival curve lies within the 95% confidence band of KaplanMeier curve. 39
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024681 0 0.00.20.40.60.81.0 024681 0 0.00.20.40.60.81.0 timesurvival probability 2 1 1. KaplanMeier 2. CoxPH Figure 3.4 CoxPH VS. KaplanMeier for RT+Tam Thus, we can conclude from the abov e analys is that CoxPH model with interactions gives a better prediction of relapse possibility of breast cancer patients in RT+Tam arm comparing to the three AFT models. Similarly, we proceed to perform a surviv al analysis of the relapse time for the patients who are treated with tamoxifen only. Figures 3.5, 3.6 and 3.7 shows the survival curves obtained from lognormal, exponential and Weib ull AFT models. It is clear that those survival curves fall out of the 95% confid ence limits of the KaplanMeier curve most of the time. Ho wever, in Figure 3.8 which shows the survival curve obtained from the CoxPH model with in teractions, we can see the survival curve lies within the 95% conf idence band. Therefore, we can conclude 40
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that for patients who received tamoxifen only, CoxPH model with interactions gives a more precise prediction of the relapse time than AFT model. 024681 0 0.00.20.40.60.81.0 024681 0 0.00.20.40.60.81.0 Timesurvival probablity Figure 3.5 Lognormal VS. KaplanMeier for Tam 024681 0 0.00.20.40.60.81.0 024681 0 0.00.20.40.60.81.0 Timesurvival probablity 1. KaplanMeier 2. Lognormal 1 1 2 2 1. KaplanMeier 2. Exponential Figure 3.6 Exponential VS. KaplanMeier for Tam 41
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024681 0 0.00.20.40.60.81.0 024681 0 0.00.20.40.60.81.0 Timesurvival probablity 1 2 1. KaplanMeier 2. Weibull Figure 3.7 Weibull VS. KaplanMeier for Tam 024681 0 0.00.20.40.60.81.0 024681 0 0.00.20.40.60.81.0 timesurvival probability 2 1 1. KaplanMeier 2. CoxPH Figure 3.8 CoxPH VS. KaplanMeier for Tam 42
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Since CoxPH model gives better prediction of relapse possibility than AFT models for both groups, we recommend CoxPH model to approximate the probability of having 2year, 5year, and 8year reoccurrencefr ee and the results are shown in Table 3.3 below. Table 3.3 Reoccurrencefree Probability 2year 5year 8year RT+Tam KM 0.98 0.95 0.93 CoxPH 0.98 0.97 0.95 Tam KM 0.94 0.88 0.76 CoxPH 0.97 0..92 0.84 Although there is consistency on indentif ying significant prognostic factors for reoccurrence of breast cancer, it c an be seen from the above six graphs, regression model might not be a good choi ce for predicting purpose. CoxPH models with interactions show more e fficiency over regression models with respect to predicting power So it would be advisable to use CoxPH model with interactions to predict the relapse time of a breast ca ncer patient given all the information of the attributable variabl es. And as can be seen form the reoccurrencefree table, patients with combined tr eatments have higher possibility of free of reoccu rrence of cancer than those with single treatment. 43
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3.4 Cure Rate Statistical Model 3.4.1 Model introduction Any clinical trial consists of a heter ogeneous group of pati ents that can be divided into two groups. Those who respond favorably to the treatment and become insusceptible to the disease are called cured. The ot hers that do not respond to the treatment remain uncured. It would be of interest to determine the proportion of cured patients and study the causes for the failure of the treatment or reoccurrence of the disease. Unlike the above mentioned survival parametric regression model and semiparametric CoxPH model with interactions that assume each patient is susceptible to failu re of treatment or reoccurrence, cure rate statistical models are survival models consisting of cured and uncured fractions. These models are being widely used in analyzing cancer data from clinical trials. The first model to esti mate cure fraction was developed by Boag (1949) which is called mixture model or standard cure rate model. Let denote the proportion of cu red patients and 1is the proportion of uncured patients, then the survival function for the group is given by ()(1)()uSt St where is the survival function of the uncured group. ()uSt 44
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It follows that the density function is given by ()(1)()u f tf t For uncured patients, we assume that the failure time or relapse time Tfollows a classical probability dist ribution, and also we can add the effect of covariates into the model using the parametric survival regression models that we studied in the previous section. For cure rate it can either be assumed constant or dependent on covariates by a logistic model, that is, 'log()exp() 1 x Thus, covariates may be used either in cure rate or in the failure time probability distribution of the uncured patients. These different conditions will be considered in developing the m odeling process. Estimates of parameters in the model c an be obtained by maximizing the overall likelihood function given by 1 1(1)()(1)()iin iiuiiiuiLf tSt where is the observed relapse time, and iti is the censoring indicator with i =1 if is uncensored and iti =0, otherwise. 45
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3.4.2 Model results for the breast cancer data For the survival regression part, We ibull, lognormal (Lnormal), Gamma, generalized loglogistic (GLL), loglogistic(Llogistic ), generalized F(GF), extended generalized gamma(EGG) and Rayleigh parametric regr ession are used. The following cases encompass the above statistica l analysis as set forth. Case 1: No covariates in and : when both cure rate and survival curve of uncured groups are independent of covariates. But we get very different cure rates using different distributions which su ggest the model is very sensitive to the underlying distribution of the failure time of uncured patients. ()uStCase 2: No covariates in six single covariates in : when we consider covariates in survival function of uncur ed group, table 3.4 shows there is some kind of consistency of cure rate am ong different distribution assumptions. ()uStTable 3.4 Cure Rate of Uncured Patients RT+Tam Tam Likelihood Cure rate Likelihood Cure rate Weibull 98.9810 0.1000 171.2401 0.0748 Lnormal 96.6371 0.0057 171.4864 0.0748 Gamma 95.9291 0.0064 171.6280 0.449 GLL 96.6900 0.1000 171.3320 0.0748 46
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Llogistic 100.6583 0.1000 171.6338 0.0748 GF 96.2180 0.002152 171.9223 0.0748 EGG 95.6891 0.0038 167.6022 0.5582 Rayleigh 117.5059 0.1000 204.8281 0.0748 Case 3: Six single covariates in six single covariates in : when we consider c ovariates in both cure rate and survival function of uncured group. Although we add six covariates into cure rate, there is not mu ch improvement in the likelihood and sometimes the likelihood is even lower, which suggests cure rate might not be dependent on those covariates; instead, we can consider it as a constant. ()uStCase 4: No covariates in six single covariates and their interactions in : Since there is no significant differenc e in maximum likelihood between case 2 and case 3, it shows including covariates does not improve the model much. Thus, in the following analysis, we cons ider cure rate as a constant, i.e. independent of those covariates. Table 3. 5 shows uniformity of cure rates using different parametric regression models. ()uSt 47
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Table 3.5 Cure Rate with Interactions of Uncured Patients RT+Tam Tam Likelihood Cure rate Likelihood Cure rate Weibull 100.5568 0.1000 166.6240 0.0748 Lnormal 109.4816 0.1000 167.8399 0.0748 Gamma 88.9750 0.1000 167.7902 0.0748 GLL 89.3220 0.1000 164.8092 0.0748 Llogistic 101.7427 0.1000 165.9777 0.0748 GF 89.0793 0.1000 164.6293 0.0748 EGG 90.5768 0.1000 163.8507 0.0748 Rayleigh 95.4851 0.1000 186.6157 0.0748 After computing the AIC of the above model s for each group, the smallest one for RT+Tam is Gamma, the smallest one fo r Tam is EGG. Hence, we choose mixture cure model with Gamma regre ssion for uncured RT+Tam group and with EGG regression for uncured Tam group. Fo r patients who received radiation and tamoxifen, 10% of them will be cured of breast cancer and not be subject to reoccurrence. However, for those who received tamoxifen alone, only 7.48% will be cured of breast cancer which suggests that giving radiation to breast cancer patients who take tamoxifen could pos sibly decrease the probability of reoccurrence of breast cancer. 48
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3.4.3 Conclusions By applying AFT and CoxPH m odels, the significant factor s and interactions that contribute to relapse time of a breast canc er patient receiving different treatments are identified and AFT and CoxPH gives consistent results. With respect to predicting survival curve, CoxPH model gives better fit than AFT models. Thus, given information of covariates of a gi ven breast cancer pat ient, CoxPH model with interactions can be applied to deter mine the time before reoccurrence of breast cancer. From a different perspective, cure rate model takes into consideration the fact that some part of the pat ients are cured and will never experience reoccurrence. It is found that cure ra tes for RT+Tam and Tam groups both are independent of the covariates and are different. For RT+Tam group, the cure rate is 0.1 which is higher than that of Tam group which is 0.0748. Thus, using the cure rate statistical model we conclude that patients received combined treatment of radiation and tamoxifen are more likely to be cured of breast cancer and less susceptible to reoccurrence of breast cancer than those who received single treatment. 49
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Chapter 4 Markov Modeling of Stages of Breast Cancer Patients 4.1 Background Markov chain model was first produced by Andrey Markov (1906) theoretically and has been applied in various fields such as physics, queueing theory, internet application, economics, finance, and social sciences. As an efficient way of describing a process in which an individual moves through a series of states in continuous time, it has also been extensively used in health filed where the progression of a certain disease are of great importance to both patients and doctors. In this chapter, the main objective is to investigate the progression of breast cancer patients in three different stages who took differ ent treatments, of which the first group of patients receiv ed combined treatments of tamoxifen and radiation, and the other gr oup of patients received ta moxifen alone. The three stages that we are interested in are: alive with no relaps e, alive with relapse, and death as shown in Figure 1. Even t hough breast cancer patients who have reoccurrence may be treated and recover ed from breast cancer and become alive with no relapse, due to the fa ct that the data does not include any observations of that process, we consider the second statealive with relapseas 50
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those patients who ever had relapse and are still a live, no matter they are recovered from breast cancer or not. Alive with no relapse Alive with relapse Dead Figure.4.1 Three Stages of Breast Cancer 4.2 Markov Chain Model Markov chain is a model for a finite or infinite random process sequence Unlike i.i.d model which assumes the independency of a sequence of events Xis, Markov model takes into account the dependencies between Xis. 12,...,{,}NXXXX Suppos e a random process 11,2{}{,...}ttXXXX {1,2,3,...,} Ss of random variables taking values in a discrete set of states andt X represents the state of the process of an individual at time In this study, there are three states: alive without relapse, alive with relapse and death and the arrows in Figure.1 show which transitions are possibl e between states. Consider a realization of the entire history of the process up to and including time t i s t111{,,...,}tttt1 X xXxXxwhere 11,,...,tt x xx is a sequence of states at different times. A random process is called a Markov Chain if the conditional probabilities 51
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between the outcomes at differe nt times satisfy the Markov property, that is, the conditional probability of an event one step into future conditioned on the entire past of the process is equal to the conditional probability of the future event given just the present. In other words, t he onestep future state depends only on the current state: t, For every sequence 11 111111(,,...,)()tttttt tttPXxXxXxXxPXxXx 11,...,,tt x xx of elements of and every probability from state to state S1t. The transition i j at time and transition intensity is defined as t 1()()ij t t p tpXjXi 0(()()) ()limij hPXthjXti qt h If the transition probabili ties do not depend on time, ()ij p t can simply be written asij p then the Markov chain is called timehomogeneous. A transition probability matrix () Ptconsists of all the transition probabilities between states in the matrix form 1112 1 2122 2 12()()...() ()()...() () ............ ()()...()s s ssss p tptpt p tptpt Pt p tptpt 52
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where probabilities in each row add up to 1. The transition probability matrix can be calculated by taking the matrix exponential of the scaled tr ansition intensity matrix ()() PtExptQ where 1112 1 2122 2... ... ............ ... s s 12 s sqqs sqqq qqq Q q The exponential of a matrix is defined by A23()1/2!/3!... ExpAAA where each summand in the series is matrix products. and corresponding states Next, the intensity matrix and transition probabilities matrix can be obtained by maximizing the likelihood Consider an individual consist of a series of times () LQ12(,,...,)nttt 12(,,...,)n x xx i. More specifically, we consider a pair of successive states observed to be and j at time and Three (1) If the information of the individual are obtained at ar bitrary observation times and the exact time of the transition of st ages is unknown, the contribution to the likelihood from this pair of states i s itjtscenarios are considered as follows. 53
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()ijijjiLptt (2) If the exact times of transitions between different states are recorded and there is no transition betw een the observation times, the contribution to the likelihood from this pair of states is (ijjpt )ij iijLtq (3) If the time of death is known or jdeath h we denote by but the state on the previous instant could be any possible state between state and death), the contribution to t he likelihood from this pair of states is before death is unknown whick(ki()ikjikj kjpttqijL After the likelihood function is constructed, the estimated intensity and maximize . For t he patients in Tam group, 51 patients () LQ () LQtransition probabilities woul d be the ones that 4.3 Breast Cancer Markov Chain Results The breast cancer patients are divided into two groups RT+Tam and Tam based on the different treatment they receiv ed. For those patients who received combined treatments, 26 patients experienc ed relapse, 13 patients died without reoccurrence of breast cancer during the entire period of study, 14 died after reoccurrence of breast cancer 54
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experienced relapse, 10 died without reoccu rrence of breast cancer, 13 died after reoccurrence of breast cancer. After r matrixes for both groups are obtained as shown in the tables below. able.4.1 Transition Intens ity Matrix of RT+Tam State 1 State 2 State3 unning the Markov model, the transit ion intensity T State 1 0.02301 0.01957 0.0034 State 2 0 0.3074 0.3074 State 3 0 0 0 able.4.2 Transity Matri State 1 State 2 State3 T nsition Inte x of Tam State 1 0.03917 0.03528 0.003889 State 2 0 0.08533 0.08533 State 3 0 0 0 As we can observe from the two tables patients who received single treatment are have a higher transition in tensity form State 1 to Stat e 2, thus they are more likely to have breast cancer reoccurrenc e. For those patients who died without relapse, there is not much significant difference between the two treatments as illustrated by the intensity form State 1 to State 3. Combined treatment is also 55
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more effective than single treatment wit h respect to the possibility of death without relapse as can be seen from the transition intensit y from State 1 to State 3. However, for those who already experienced relapse of breast cancer, patients who received combined treatments are more likely to die than those who received single treatment. In other words, combined treatment should be chosen over single treatment to avoid reoccurr ence, but for those patients who already had breast cancer relapse, it would be advisable to choose single treatment to extend the time from reoccurrence to death. l probability. The two graphs show the survival curves of the patients who had reoccurrence and who had no reoccurrence in each treatment group. for Tam group in Figure 3 which suggests combined treatment of tamoxifen and radiation is not as effective as radiation alone for patients who had reoccurrence. The following two graphs give a clearer view of the effectiveness of the two treatments with respect to the surviva Comparing the above two graphs, it is clear that for patients who are in State 2 (ever experienced reoccurrence of breast cancer), the curve for RT+Tam group in Figure 2 has a much faster decreasi ng slope than the curve 56
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02468 0.00.20.40.60.81.0 TimeFitted survival probability From state 1 From state 2 Figure.4.2 Survival Curves of Patients in RT+Tam 024681 0 0.00.20.40.60.81.0 TimeFitted survival probability From state 1 From state 2 Figure.4.3 Survival Curves of Patients in Tam 57
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From the above analysis, Markov chain model gives us recommendations on which treatment to choose for breast canc er patients with respect to relapse and survival time. Moreover, it provides pat ients with very important information on the exact time or possibilities of reoccurrence and death. Estimated mean sojourn times in each transient st ate for patients who received combined treatment are 43.46 and 3.25 in State 1 and State 2, respectively. Estimated mean sojourn times for patients who re ceived single treatment are 25.53 and 11.72 in State 1 and State 2. This further confirms ou r conclusion that patients with combined treatment will stay in St ate 1 longer than those with single treatment, however, for pati ents who had relapse of brea st cancer, patients with single treatment with stay alive longer than those with combined treatment. Another major concern of this study is to provide transition probability matrix at different times so th at given specific time period, we will be able to tell the probability that a given state will transit to anot her state. Tables 3 to Table 10 give 2year, 4year, 5year and 10year tr ansition probability matrixes of patients in RT+Tam and Tam groups. Table 4.3 2year Transition Probability for RT+ Tam Stage 1 Stage 2 Stage 3 Stage 1 0.9550 0.0285 0.0165 Stage 2 0 0.5408 0.4592 Stage 3 0 0 0 58
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Table 4.4 2year Transit ion Probability for Tam Stage 1 Stage 2 Stage 3 Stage 1 0.9247 0.0623 0.0130 Stage 2 0 0.8431 0.1569 Stage 3 0 0 0 Table 4.5 4year Transition Probability for RT+Tam Stage 1 Stage 2 Stage 3 Stage 1 0.9121 0.0426 0.0453 Stage 2 0 0.2925 0.7075 Stage 3 0 0 0 Table 4.6 4year Transit ion Probability for Tam Stage 1 Stage 2 Stage 3 Stage 1 0.8550 0.1102 0.0348 Stage 2 0 0.7108 0.2892 Stage 3 0 0 0 Table 4.7 5year Transition Probability for RT+Tam Stage 1 Stage 2 Stage 3 Stage 1 0.8913 0.0466 0.0621 Stage 2 0 0.2151 0.7849 Stage 3 0 0 0 59
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60 Table 4.8 5year Transit ion Probability for Tam Stage 1 Stage 2 Stage 3 Stage 1 0.8221 0.1295 0.0484 Stage 2 0 0.6527 0.3473 Stage 3 0 0 0 Table 4.9 10year Transiti on Probability for RT+Tam Stage 1 Stage 2 Stage 3 Stage 1 0.7945 0.0515 0.1540 Stage 2 0 0.0463 0.9537 Stage 3 0 0 Table 4.10 10year Trans ition Probability for Tam Stage 1 Stage 2 Stage 3 Stage 1 0.6759 0.1910 0.1331 Stage 2 0 0.4260 0.5740 Stage 3 0 0 0
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4.4 Conclusion Through Markov chain modeling of the thr ee stages of breast cancer patients: alive with no relapse, alive with relaps e, and death, it shows that combined treatment of tamoxifen and r adiation is more effective than single treatment of tamoxifen in preventing the reoccurrence of breast cancer. However, for patients who had relapse of breast cancer, single tr eatment of tamoxifen proves to be more effective than combined treatment wi th respect the survival probability. Transition probabilities between different stages during 2 years, 4 years, 5 years and 10 years are also construc ted for predicting purpose. 61
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Chapter 5 Statistical Comparison of Breast Cancer Patients with Different Histology Types 5.1 Background and Data The relapse time and survival time of br east cancer patients could be different between groups who receive different treat ment. Another importa nt factor that should be taken into consideration is the histology type of br east cancer patients. In order to see the effect of histology type of breast cancer patients on survival time, relapse time, the previous ment ioned data is divided into the following several subgroups shown in the Figure 5.1 based on the histology type and treatment they received, t hose 641 breast cancer patient s can be divided into the following several subgroups shown in Figure 1 for later analysis. It can be noticed that the majority of the breast cancers are ductal (3 97) or mixed(174), only a small number are lobular (31), medullar(5), mucinous (16) or others(18). 62
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Total (641) DUC (397) LOB (3 1) MIX ( 174) MED (5 ) MUC (1 6) OTH (1 8) 63 RT (203) TAM ( 194) RT (1 7) TAM (1 4) RT (8 2) TAM (9 2) RT (1 ) TAM (4 ) RT (8 ) TAM (8 ) RT (10) TAM (8 ) Figure 5.1.Breast Cancer Patients Grouped by Histological Types and Treatments Information concerning potential prognostic factors (attributable variables) are pathsize (size of tumor in cm); hist ( Histology : DUC=Ductal, LOB=Lobular, MED= Medullar, MIX=Mixed, MUC=mucinous, OTH= Other); hrlevel (Hormone receptor level: NEG=Negative, POS=Positive); hgb (Hemoglobin g/l); nodediss (Whether axillary node dissection wa s done: Y=Yes, N=No); age (Age of the patient in years). The response variables we are inte rested in are survival time and relapse time of a given patient. In the next several sections, related research of breast cancer based on the same dataset is first reviewed, then we proceed to addresses the following questions: is there a difference of survival curves between different histological types; is there a difference of relapse time between different hi stological types; do patients of different cancer types react differently to treatments with respect to survival time and relapse time?
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Despite the usefulness of the previous work done on the dataset, it does not take into consideration of the possible different behavior of different histological breast cancer types. For example, patients wit h different cancer type would react differently to the same treatments, and also there are pot ential significant differences among various cancer types wit h respect to survival time and relapse time. In this study, we divide the datas et into several subgroups based on the histology of the tumors as shown previ ously, and confine our study to the major two breast cancer types: ductal (DUC) and mixed (MIX) to address the following questions: 1. Is there significant difference for survival time among different histological breast cancer types? 2. Is there significant difference for relapse time among different histological breast cancer types? 3. Do patients with different histological breast cancer types react the same way to treatment with respect to survival time and relapse time? 5.2 Comparison of Survival Time and Relapse Time It is of importance to see if the survival curves of patients in different cancer types are the same. Thus KaplanMeier [8 ] curves are plotted for each of the three major breast cancer types. KaplanMeier estimates of the survival curves of relapse time for the two treatment groups are shown in Figure 5.2. 64
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02468 1 0 0.00.20.40.60.81.0 timesurvival probability 02468 1 0 0.00.20.40.60.81.0 timesurvival probability DUC ___ MIX .. Figure 5.2. KaplanMeier Curves of Survival Time in DUC and MIX As seen from the graph, the two curves almost overlap showing there is not much difference for survival time of the tw o breast cancer types. To verify that, Logrank test is applied and pvalue of 0.693 showing that there is no significant difference between survival curves of ductal breast cancer patients and mixed breast cancer patients. This suggests that there is homogeneity of survival time with respect to breast cancer types, so when analysis is conducted on survival time of breast cancer patients, there is no need to separate data into subgroups based on histology type. Similar analysis is conducted for relapse time and the KaplanMeier survival curves are shown in Figure 5.3 below. 65
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02468 1 0 0.00.20.40.60.81.0 timesurvival probability 02468 1 0 0.00.20.40.60.81.0 timesurvival probability DUC ___ MIX .. Figure 5.3. KaplanMeier Curves of Relapse Time in DUC and MIX Furthermore, pvalue 0.516 of Logrank test indicates that there is no significant difference of relapse curve between Duct al and Mixed breast cancer patients. 5.3 Treatment Effectiveness of Different H istology From the previous analysis we find that histology type does not affect the survival and reoccurrence behavior of breast cancer patients. Therefore, we proceed to investigate the treatment effects in differ ent histology types. In another words, we are interested in if combined treatment and single treatment affect survival and relapse time in the same pattern fo r breast cancer patients with different histological types. 66
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First, the survival curves of survival time and relapse time of patients of combined treatment group (RT+Tam) and single treatment group (Tam) are compared to see the overall effectiveness of the two treatments. For survival time and relapse time, the KaplanMeier curves are shown in Figure 5.4 and 5.5 below. And the pvalues of the Logrank test are 0.379 and 0.00192 for survival time and relapse time, respectively. Under significance level of 0.05, it can be concluded that there is no significant difference for su rvival time between the two treatments. However, combined treatm ent seems to be more effective than single treatment with respect to relaps e time of breast cancer patients. 024681 0 0.00.20.40.60.81.0 timesurvival probability 024681 0 0.00.20.40.60.81.0 timesurvival probability RT+TAM ___ TAM .. Figure 5.4. KaplanMeier Curves of Survival Time in RT +TAM and TAM 67
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024681 0 0.00.20.40.60.81.0 timesurvival probability 024681 0 0.00.20.40.60.81.0 timesurvival probability RT+TAM ___ TAM .. Figure 5.5. KM Curves of Relapse Time of RT+TAM and TAM Same analysis is conducted to the pat ients groups determined by various histology types. As mentioned above, we confine our analys is to the major two histological types: ductal and mixed bec ause the other histology types do not have enough number of observations for st atistical analysis. After running Logrank test for survival time and relapse time with respect to two different treatments of each histology type, the pvalues are obtained and listed in Table 5.1. 68
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Table 5.1. Logrank Test for Survival Time and Relapse Time Histology Type DUC MIX Survival/Relapse Survival Time Relapse Time Survival Time Relapse Time Pvalue 0.217 0.0114 0.708 0.0256 As can be observed from Table 5.1, for patients in both DUC and MIX group, survival time of patients who received combined treatment does not significantly differ from those who received single treat ment. However, t here is significant difference for relapse time between different treatment groups within both DUC and MIX cancer types. This result is cons istent with the result obtained from the complete data that consists of all hist ology types. Thus, breast cancer type does not affect the choice of treatment with re spect to survival time and relapse time. 5.4 Conclusion Previous research on real breast cancer data is reviewed and the question of homogeneity among different breast cancer histology types is brought into consideration. By dividing the data based on histology type, KaplanMeier curve and Logrank test are perform ed to test the homogeneity of survival time, relapse time, and treatment effect between the two major histology types: ductal and mixed. Results show there is no significant difference for survival time and relapse time between this two histology types of breast cancer, and treatment 69
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effect is the same between the two breast cancer types as well. Thus, there are no significant treatment effects with respec t to survival time for DUC, MIX, and the totality data, and combi ned treatment is more effe ctive than single treatment with respect to relapse time for DUC, MI X and the totality data. This finding provide useful information for statistica l analysis and modeling of breast cancer data in the way that all t he observations from differe nt histology types can be analyzed as a combined dataset because of the homogeneity among different histology types instead of splitting them into subgroups, and could effectively reduce the time and effort spent on modeling of breast cancer data. 70
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Chapter 6 Sensitivity Analysis of Br east Cancer Doubling Time 6.1 Background Growth rate of breast cancer tumors is a critical aspect to understanding the natural history of breast cancer and doubling time (DT) is most commonly used to indicate how fast tumors grow. To be more specific, doubling time is the time it takes for a tumor to double in size. With res pect to that objec tive, we need to identify the geometrical behavior of the tumo r so that we can obtain an estimate of its volume, we need to identify the math ematical behavior of the growth of the tumor and once we have determined the doubling times, we need to obtain the best possible fit of a probability distribution that characterizes their behavior. Peer P. G. M. et. al in an article concer ning age dependent growth rate of primary breast cancer assumed one of four possibl e geometrical formulas to calculate the volume of the tumor. If we consider any of the others that are also commonly used, the overall results will be different. They also assumed exponential growth of the tumor when in fact actual data reveals that t he tumor growth is decaying exponentially up to the age of 48, then it follows a quadratic growth between the age 49 and 68, and then follo ws a exponential growth up to age 100. Thus, assuming exponential growth for all ages will lead to misleading decisions. 71
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Furthermore, in the subject paper, they a ssumed that the doubl ing time follows a two parameter lognormal probability dist ribution. However, our goodnessoffit statistical testing shows t hat the lognormal is not the best probability distribution. The methodology and results of the subject article l ead to a sequence of other publications. Most recently, Green, L. (2009), in a conference pr esentation, Age Dependent Screening used Peers et al. results in their research on the subject matter, that is exponential growth of the tumor, the same geometri cal volume formula and the lognormal probability distribut ion of the doubling time. Thus, the results that followed are subject to the above comments. However, it is rarely possible for m edical doctors to obtain the exact doubling time of a given breast cancer patient since there is no record of two mammograms of which the volume of larger tumor is exactly twice as large as the other of one given patient. Thus, we need to assume the shape of the tumor to estimate the volume of the tumor, and prespecify the tumor growth model to estimate the doubling time. As a result of different volume and growth model assumptions, the probabi lity behavior of doubling ti me can be significantly different. In the present study we shall consider the four commonly used formulas to measure the volume of t he tumor, in conjunction with negative exponential, linear and quadratic growth behavior of the tumor as a function of age. For each case we will calculate the doubling time and proceed to identify the appropriate 72
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probability distribution for parametric analysis. Thus, having these various scenarios a physician can make the optimal decision co ncerning his patients. In other words, the following questions are addressed: 1. What is the mathematical growth behavior of breast tumor as a function of age? 2. What are the time (age) intervals that have the same analytical form of the average tumor growth? 3. What is the best mathematical expression that bes t characterize the behavior of the average tumor size for s pecific time (age) intervals? 4. Can we use these analytic al characterizations of the average tumor size to predict or estimate the rate of tumor growth as a function of age? 5. Are the four different commonly used volumes to determine doubling time robust with respect to the analytical form of the growth of the tumor? 6. Do the resulting doubling time of the twelve possible configurations of volume and analytical form of the average size of tumor results in the same probability distribution? 7. Can we justify using the standard lognormal probability distribution for any of the four volumes or different analytic al growth of the average tumor size? 73
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8. How are the current findings compared with the commonly used standard lognormal probability distribution to characterize the probabilistic behavior of the doubling times? 6.2 Breast Cancer Data The present data was first used by Heuser et.al. (1979) where 108 women underwent screening for breast cancer at the Breast Cancer Detection and Demonstration Project conduct ed at the University of Louisville. All of these 108 women received mammography as thei r screening method among which 45 were diagnosed on the initial mammo graphy; thus, there is no previous mammography record. Howe ver, for the remaining 64 women, 32 had two or more mammograms based on which we conduct the subject study on tumor growth. For each of these 32 patients, the mammograms were displayed in series, and measurements of the major axis (a) and minor axis (b) are obtained from the mediolateral views as shown in Figure 6.1 and the details are listed below in Table 6.1. It is cl ear that there is no growth of breast tumor in 4 patients. 74
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Breast Cancer Patients (32) Initial Date Second Date Figure 6.1 Breast Cancer Mammogram Data Table 6.1 Date and Dimensions of Tumor Observations Patient ID Initial Date Initial Dimension (mm) Second Date Second Dimension (mm) 1 04/25/75 12*11 01/06/76 30*14 2 10/15/74 22*17 01/15/75 27*20 3 01/30/74 10*8 01/28/75 22*15 4 10/14/74 7*5 07/10/75 16*8 5 04/12/76 30*20 04/28/77 70*28 6 08/29/73 6*3 02/11/75 20*5 7 11/08/73 20*7 11/21/74 30*12 8 06/04/75 13*10 06/18/76 18*16 9 01/02/75 30*15 04/01/75 40*15 10 01/24/74 6*5 01/10/75 18*5 ( ) 1t(2) t Major Axis (a) Minor Axis (b) Major Axis (a) Minor Axis (b) 75
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11 07/17/75 15*15 07/21/76 26*22 12 02/24/76 5*4 07/22/76 8*4 13 03/17/75 8*6 03/09/76 12*8 14 10/09/75 11*8 09/22/76 12*12 15 11/18/74 13*11 11/07/75 20*13 16 01/07/75 18*15 05/29/75 18*17 17 06/23/75 20*18 04/02/75 25*20 18 02/11/75 12*11 01/09/76 20*15 19 10/24/74 18*7 06/23/76 19*9 20 03/23/75 70*70 02/24/76 90*80 21 10/24/74 22*12 10/09/75 24*14 22 03/23/75 18*10 04/01/77 21*11 23 02/20/75 10*6 02/24/76 13*6 24 10/08/75 25*17 04/01/76 25*17 25 12/06/74 5*3 03/07/75 5*3 26 06/26/75 6*5 12/10/75 6*5 27 02/01/75 8*6 08/01/75 9*6 28 06/03/75 18*13 06/04/76 19*13 29 08/03/74 10*8 08/10/75 11*8 30 02/06/75 6*6 02/23/76 7*6 31 01/30/74 38*27 01/28/75 44*26 32 07/15/74 20*12 08/01/75 20*12 76
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The above table identifies the patient data of first and second mammograms along with the major & minor axis. 6.3 Geometrical Formulas of Tumor Volume In the present study we wil l investigate the volume of the breast tumor that is commonly used in the subject matter. Spherical Shape: 33 4 rV ; where r is the radius calculat ed from the major axis, 2/ar with a being the major axis. This formula is commonly used for purpose of simplicity as in Hesuers paper and Greens presentation. Averaged Spherical Shape: 33 4 rV The radius r is the average of t he major and minor axis, 6 2 ba r where a is the major axis and b is the minor axis. This formula assumes the same shape of tumor but takes into consideration the two measurements inst ead of focusing on 77
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only one dimension of the tumor. This form of the volume was also used in Hesures paper. Oblate Spheroid: ) 2 () 2 ( 3 42ba V This formula assumes different shapes of volume as the two above. However, it gives more emphasis on the major axis. This formula is also mentioned in Hesures paper. Averaged Oblate Spheroid: ) 2 1 2 1 ( 2 1 2 1 2 1 3 4 baba V This formula uses the average of major and minor axiss, thus gives equal weight to the two measurements as used in Peer, et. al (1993) publication We shall study each of these volumes separ ately with respect to different growth rate of the tumor and the resulting probabi lity distribution of the doubling time. Figure 6.2 below shows a sca ttered diagram of the aver age breast tumor size as a function of the age of the cancer patients. 78
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20 40 60 80 100 10 20 50 40 30 average tumor size A ge (in years) Figure 6.2 Average Tumor Size VS. Age It is clear from the above scattered diagram that the mathemat ical configuration over all the ages is different. Thus, we shall group the average tumor size into three age groups. First group starts from 17 to 48, the second group from 49 to 78, and the last one from 79 years old and on. The first group clearly shows an exponential decay, and then flat linear or quadratic decrease and then exponential increase. Thus, we shall appr oximately partition the average tumor sizes into three groups as mentioned above and proceed to identify the best mathematical fitting function of the obser ved data in each of the three regions. We begin by graphing respectively the th ree age intervals, the first being from age 17 to 48. Figure 6.3 gives a better di agram of the data in that interval. 79
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20 25 30 35 40 45 50 10 20 30 40 50 age (in years) 20 25 30 35 40 45 50 10 20 30 40 50 average tumor size Figure 6.3 Average Tumor Size with Age 1748 The best mathematical function that descri bes breast tumor size as a function of age in this interval is given by tetf015254.042)(, 17 48 t. A residual analysis supports that gives a good fit of the breast tumor growth in the given interval. Furthermore, we can differentiate the above equation with respect to t, and evaluate it in a s pecific age of interest to identify an estimate of the rate of growth of the size of the breast tumor. )( tf 80
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The scattered diagram of the breast tumor size between the patients age between 49 and 78 is shown below by Figure 6.4. Figure 6.4 Average Tumor Size with Age 4978 Thus, visually it could be approximated by either a linear or quadratic function and therefore, we will include both in our statistical anal ysis. If we assume it is linear, the best estimate is given by t tf 05925.067865.22)(, 7849 t. 50 55 60 65 70 75 80 age (in years) 50 55 75 80 60 65 70 20 22 24 20 22 24 average tumor size 16 18 16 18 81
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The quadratic function form of the aver age breast tumor size in the second interval is given by 200547.0 764531.0014257.45)( t t tf 7849 t. Residual analysis reveals that the analyt ical quadratic function gives a better fit than the linear function. However, sinc e some medical scientist use the linear function, we will include it in the present analysis. Finally, the scattered diagram for breast cancer patients older than 78 years old is given by Figure 6.5 below. It is clear that the breast tumor size sl owly increases exponent ially after the age of about 78 years old. The best mathematical form that fits the tumor growth behavior in this age interval is given by te tf033947.0208443.1)(, 78 tResidual analysis that we performed suppo rts the quality of the fit for the given function in the third age interval. Again, once we have identifi ed the analytical function form of the size of the breast tumor, we can differentiate it with respect to time (age) and evaluate at a specific age to determine t he change of the tumor size. Now we will proceed to obtain the doubling time for each volu me and growth rate we have identified. 82
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83Figure 6.5 Average Tumor Size with Age above 78 6.4 Analytical Calculation of Doubling Time After having identified the best possible analytical form of the average size of breast tumor as a function of age, we can proceed to calculate the doubling time of tumors. Since we only have two observations of each patient, for the growth function, we have to be specific so t hat there is only one parameter in the function. First, we have to choose the suitable geometric volume of the tumor and obtain the corresponding initial volu me and second observation of volume. 60 60 average tumor size 5 50 40 40 30 30 20 20 95 95 80 80 85 85 90 90 100 100age (in years)
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After that we will see the calculation of the doubling time of breast tumor based on different growth assumptions. Under linear growth, the following relation between two observations from a given individual can be obtained: tVVo 1. Thus, t VV01 and 01 0 01 0 0002 VV tV t VV VVVV DT Estimates of and DT in the above equations will be obtained using actual data. Quadratic growth model takes into c onsideration the quadratic growth with respect to time. As mentioned above, si nce there are only tw o observations of each patient, only one parameter is in volved in the quadratic function. 2 01tVV. Thus, 84
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2 01t VV and 01 0 01 0 0 002 VV tV t VV VVVV DT Under exponential growth, the follo wing growth model can be obtained: )exp(0tVV Where is the initial tumor size, and oV and doubling time DT can be obtained as t VVolnln1 and 2ln DT The above two expressions are the true an alytical forms and we will use actual data to obtain the approximate estimates. Thus, we will use the derived analytical forms of DT for the four different volumes to obtain the actual doubling times. 85
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If we use the finding that the breast tumors follow linear growth, we can calculate the doubling times under each of the four different volu mes: spherical; averaged spherical; oblate spherical; averaged obl ate spherical. The results of the calculated doubling times are shown in Tabl e 6.2. Because the last observation has no change in major axis, thus there is no change in spherical volume which causes the doubling time not applicable. Table 6.2 Doubling Time under Linear Growth Spherical Average Spherical Oblate Spherical Averaged Oblate Spherical 17.50427 64.57835 83.94580 50.32479 108.42457 129.10155 131. 68303 124.32018 37.62438 51.85714 53.90255 48.53482 24.58487 47.44559 55.44759 42.60181 32.55380 78.84934 106.62313 70.52073 14.73484 36.30769 64.29148 36.79299 159.15789 125.73555 110. 91018 126.00000 229.67263 153.33034 149. 33495 192.76923 64.94595 151.37008 267.00000 167.03911 13.50000 80.51613 175.50000 141.35294 87.93395 133.86104 135.60104 66.56897 48.12661 172.38178 248.33333 120.61721 86
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150.73684 205.27523 214. 80000 131.47059 1170.07305 254.67568 239. 93750 327.08969 134.02344 278.69026 308. 15827 236.00000 201.44262 523.18977 499. 21875 702.90000 100.28571 340.55765 353. 45455 297.79592 2078.39533 166.94660 173. 40157 148.05788 335.89119 670.56684 491. 34247 703.84615 1173.42569 550.07197 556. 45494 481.98513 1258.58268 787.28970 721. 87500 828.48101 308.27068 1648.27603 1797. 57085 1585.71429 427.05991 789.45389 1230. 00000 678.62069 2084.07400 1148.29500 1448. 00000 881.39130 1123.86707 5262.16597 6606. 00000 4095.72000 649.70079 3103.11913 3720. 00000 2308.96552 657.11718 2169.25414 2292. 00000 1447.57895 NA 2665.43211 4924.49853 1807.95146 Similarly, for the quadratic growth of the breast tumors, we can calculate the doubling times under each of the four diff erent volume formulas: spherical; averaged spherical; oblate spherical; aver aged oblate spherical. The results are given in Table 6.3 below. 87
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Table 6.3 Doubling Time under Quadratic Growth Spherical Averaged Spherical Oblate Spherical Average Oblate Spherical 66.94097 128.5771 146.5951 113.5039 99.87522 108.9832 110.0674 106.946 116.866 137.2011 139.8808 132.7333 81.32238 112.9728 122.1286 107.0509 111.3687 173.3251 201.5525 163.9158 88.45451 138.8502 184.7668 139.7751 245.2788 218.0093 204.7536 218.2384 295.4244 241.3825 238.2169 251.9422 76.02756 116.0687 154.1525 112.1624 68.83676 168.1106 248.1945 152.8585 180.3762 222.5502 223.9919 211.2543 84.68096 160.265 192.3582 139.9611 232.3011 271.0877 277.3056 262.7002 639.027 298.1305 289.3755 337.8673 217.8171 314.0961 330.2848 289.0398 196.6647 272.5673 266.25 315.9301 191.0602 255.709 260.5058 239.1167 872.177 246.5128 251.2333 232.1488 88
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356.3241 495.4064 424.0653 507.5507 640.858 455.9904 458.6284 426.8376 965.0654 524.9299 502.6492 538.4871 337.2712 1104.411 1153.344 1083.249 278.0249 539.73 673.6987 500.4109 874.56 455.8963 511.9453 399.4144 646.5899 1389.682 1557.049 1226.022 498.1824 1074.412 1176.367 926.7876 488.399 910.3049 935.7051 743.623 NA 983.6421 1337.009 810.115 Finally, as we have shown that in the third age interval, for patients older than 78 years of age, the breast tumor growth follows the exponential function we can calculate the doubling times under each of the four different volume formulas: spherical; averaged spherical; oblate s pherical; averaged oblate spherical. Table 6.4 Doubling Time under Exponential Growth Spherical Averaged Spherical Oblate Spheroid Average Oblate Spheroid 64.55217 110.74799 126.8724 98.24536 103.7944 118.52572 120.358 115.1284 106.3733 121 122.9973 117.70724 89
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75.18303 98.26084 105.5403 93.70481 103.89462 149.7647 173.7151 142.23461 101.90185 133.89533 165.3744 134.50317 215.39842 188.78535 176.6209 189 269.79901 211.30055 208.1474 222.0329 71.47948 133.39783 214.4385 126.32282 73.81878 144.91768 221.4563 132.49819 155.41991 193.48532 194.8772 182.79169 73.2469 165.79857 219.7407 136.30841 204.00168 245.83176 252.9968 236.37022 926.73079 280.29596 269.4032 333.1652 189.86678 299.2805 320.7961 267.79066 198.80216 409.89326 393.1944 534.91821 198.80216 297.65657 306.7415 267.46283 1564.0522 218.07114 223.0551 203.33541 347.51902 582.46856 455.7098 605.88872 929.38618 500.91682 505.442 452.51952 1109.1505 659.58923 613.6952 688.45059 324.957 1383.1473 1487. 7378 1339.2671 355.0586 666.93933 974.871 1339.2671 1568.3256 857.13751 1065. 1758 671.71212 901.79507 3773.2189 4704. 9767 2964.3103 572.56148 2277.4113 2705. 3852 1726.1698 90
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572.09291 1632.4261 1717. 6844 1130.6136 NA 1970.6666 3537. 7173 1375.1483 6.5 Probability Distribution of Doubling Time Now that we have calculat ed the doubling time for each configurations of tumor growth behavior and the different volume of the tumor as shown in Table 6.2, 6.3 and 6.4, we will proceed to identify the bes t possible probability distribution that characterizes the probabilistic behavior of t he doubling time. That is, we want to statistically using general goodnessoffit test to identify the best possible probability distribution that characterize s the behavior of the doubling time. To find the best probability distribution, we utilize three different types of goodnessoffit tests including KolmogorovSmir nov (1971), AndersonDarling (1952) and ChiSquare (1954) tests. Once we have identified the best possible probability distribution, we shall give the basic and useful statistics of each of the scenarios for proper and relevant interpretati on for comparison purpose along with confidence limits of the true doubling time. Use the above test criteria for goodnes soffit, we have found the following probability distribution of each growth function. Case 1. Linear Growth and Four Different Volumes 91
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(a) Linear Growth and Spherical Volume : Using the data for doubling time as given by Table 6.2 and the goodnessoffit test that we mentioned above, the best probability distribution is Fatigue Life with the following probability density function (p.d.f). /174.79174.79/1 174.79 () (( )) 21.8276 1.8276174.79 xxx fx xx (b) Linear Growth and Average Spheric al Volume: The threeparameter lognormal is the best fit distributi on whose p.d.f. is given by 27292.1)052.33( )) 7292.1 4105.5)052.33ln( ( 2 1 exp( )(2 x x xf. (c) Linear Growth and Oblate Spherical Volume: The fourparameter Pearson probability distribution is the best fit with p.d.f. 01378.7 2477.5)82.18/)447.26(1)(76608.0,2477.6(82.18 )82.18/)447.26(( )( x B x xf. (d) Linear Growth and Average Oblate S pherical: The threeparameter lognormal is the best with p.d.f. 27891.1)391.34( )) 7891.1 2388.5)391.34ln( ( 2 1 exp( )(2 x x xf. 92
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In Table 6.5 below, we have calculated the basic statistics and 95% confidence limits of the true doubling time along with the same estimates for the commonly used lognormal probability distribution for comparison purpose. As can be seen that there are signifi cant differences of the basic statistics and confidence limits between the justified p.d.f.s and the one t hat is not statistically acceptable. Table 6.5 Distribution of Doubling Time under Linear Growth Volume Distribution Mean S.D 95% lower limit 95% upper limit Spherical Fatigue Life 466.69 726.68 11.84 2580.4 Lognormal 573.99 1741.8 9.0575 3563.2 Averaged Spherical Lognormal (3P) 1030.8 4336.1 40.601 6664.9 Lognormal 769.1 1747.2 22.048 4354.5 Oblate Spherical Pearson 6 (4P) 969.97 2378.3 54.229 15768.0 Lognormal 898.33 2028.5 26.075 5074.4 Averaged Oblate Spherical Lognormal (3P) 963.54 4509.4 40.016 6284.8 Lognormal 655.05 1387.4 21.682 3607.4 93
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Case 2. Quadratic Growth and Four Different Volumes We shall use the same statistical criteria to identify the best possible p.d.f. that characterize the doubling time data given in Table 6.3. (a) Quadratic Growth and Spherical Vo lume: Using the data for doubling time and the goodnessoffit test that we mentioned above, the best probability distribution is Johnson SB with the follo wing probability density function (p.d.f). 20.500621 ()exp((0.845090.50062ln())), where 61.3031095.303 21 10342(1)x fx x x xx (b) Quadratic Growth and Averaged Sphe rical Volume: The threeparameter Frechet is the best fit distribution whose probability density function (p.d.f.) is given by )) 814.60 76.138 (exp() 814.60 76.138 ( 76.138 1887.1 )(1887.1 1887.2 x x xf. (c) Quadratic Growth and Oblate Spheric al: The Burr probability distribution is the best fit with p.d.f. 22469.17215.5 7215.4)) 19.160 (1(19.160 ) 19.160 (22469.07215.5 )( x x xf (d) Quadratic Growth and Average Oblate Spherical: The p.d.f. of the best possible probability distributi on Frechet is given by 94
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)) 1.196 (exp() 1.196 ( 1.196 5838.1 )(5838.1 58381.2x x xf The basic statistics along with the corresponding 95% confidence limits are given in Table 6.6 below. Table 6.6 Distribution of Doublin g Time under Quadratic Growth Volume DistributionMean S.D 95% lower limit 95% upper limit Spherical Johnson SB 331.47 274.66 65.101 994.63 Lognormal 336.95 345.11 44.756 1238.0 Averaged Spherical Frechet (3P)873.98 475.31 107.09 3118.6 Lognormal 403.76 350.54 70.173 1324.7 Oblate Spherical Burr 712.34 477.81 110.47 2823.9 Lognormal 435.77 374.89 76.813 1420.7 Averaged Oblate Spherical Frechet 473.19 422.42 86.007 1997.8 Lognormal 377.7 316.05 69.464 1207.9 95
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It can be observed that, under linear growth assumption as shown in the previous section, Fatigue Life is the best fitting probability distributi on. However, when quadratic growth function is considered, the bestfitting distribution changes to Johnson SB distribution, and the statisti cal properties such as mean and 95% confidence bands change as well. This suggests doubling time is sensitive to the growth assumption chosen and thus ca reful research would be done on the shape of breast cancer before assuming any probability distribution for the doubling time. Furthermore, since doubling time is used widely as an indication of how fast tumors grow, mean and 95% confidence bands give both doctors and patients useful information on the progression of a breast cancer tumor. However, these statistical properties vary significantly fr om distribution to distribution. Not only tumor shape affects the doubling time distri bution, tumor growth function also affects the way tumor volume is calc ulated and subsequently the doubling times calculated from tumor volumes as illus trated both in the table above and the analysis below. Case 3. Exponential Growth and Four Different Volumes Utilizing the same approach, we calculat e doubling times of t he 28 breast cancer patients under four diffe rent geometric shape scenarios: spherical, averaged spherical, oblate spherical, averaged oblate spherical as shown below. 96
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(a) Exponential Growth and Spherical Volu me: Using the data for doubling time and the goodnessoffit test that we mentioned above, th e best probability distribution is the thre eparameter lognormal wit h the following p.d.f. 27292.1)612.62( )) 7292.1 8435.4)612.62ln( ( 2 1 exp( )(2 x x xf. (b) Exponential Growth and Averaged Spherical Volume: The threeparameter lognormal is the best fit distribution whos e probability density function (p.d.f.) is given by 26535.1)239.95( )) 6535.1 1591.5)239.95ln( ( 2 1 exp( )(2 x x xf. (c) Exponential Growth and Oblate Spher ical: The threeparameter Frechet probability distribution is the best fit with p.d.f. )) 287.80 21.135 (exp() 287.80 21.135 ( 21.135 87589.0 )(87584.0 875841.1 x x xf. (d) Quadratic Growth and Average Oblate Spherical: The p.d.f. of the best possible probability distribution, threeparameter Fatigue Life is given by )) 284.84 88.179 88.179 284.84 ( 8229.1 1 ( )284.84(8229.12 )284.84/(88.17988.179/)284.84( )( x x x x x xf 97
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Their 95% confidence limits of the true doubling time along with those of the commonly used Lognormal probability dist ribution of each group of doubling times are given in Table 6.7. Table 6.7 Distribution of Doublin g Time under Quadratic Growth Volume DistributionMean S.D 95% lower limit 95% upper limit Spherical Lognormal (3P) 628.61 2459.9 66.894 3824.6 Lognormal 419.36 551.35 35.631 1809.0 Averaged Spherical Logrnnomal (3P) 778.0 2950.5 102.05 4542.0 Lognormal 588.58 793.94 47.653 2578.4 Oblate Spherical Frechet 770.88 1529.0 110.75 9073.2 Lognormal 685.92 983.2 49.467 3113.7 Averaged Oblate Spherical Fatigue Life (3P) 563.05 744.44 96.523 2728.1 Lognormal 543.93 699.01 48.221 2313.9 98
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From the above analysis, it is clear that the probability behavior of doubling time varies significantly with respect to the tumor volume, and under all circumstances, the popular lognormal probability distribution is far from the best fitting probability distribution that characterizes the stat istical behavior of doubling time. Besides that, there is no consistency betw een the mean and 95% confidence limits constructed from the bestfitting distributions. Thus, it is of great importance to invest igate the shape of the tumor as well as the tumor growth pattern before any statis tical analysis of the doubling time are calculated from the volume and tumor growth assumptions vary significantly from scenario to scenario. 6.6 Conclusion As a result of the present study, we can conclude that 1. The analytical growth behavior of the average breast cancer tumor size is not exponential for all age s as commonly assumed. For example, we have found that age between 17 and 48, t he growth is exponentially decaying. For ages between 48 and 78, the tumor growth is best char acterized by a quadratic analytical function. However, not quite as good as the linear behavior. And exponential growth function best fits the average tumo r size for patient older than 78 years. 2. There are four commonly used formulas for determining the volume of breast tumor, and using these four configuratio ns of the volume results in different 99
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doubling times. Thus, the resu lts are sensitive with respect to the choice of the specific volume we use. 3. Calculation of the doubl ing time of each volume and different mathematical growth results in twelve cases with different probability distribution that characterize the probabilistic behavior of the doubling time. Table. 6.8 gives a summary of the actual probability distri bution that one should use along with the types of growth rate the volume. Table 6.8 Summary of Results Spherical Averaged Spherical Oblate Spheroid Averaged Oblate Spheroid Linear Threeparameter lognormal Threeparameter lognormal Threeparameter Frechet Threeparameter Fatigue Life Quadratic Fatigue Life Threeparameter lognormal Sixparameter Pearson Threeparameter lognormal Exponential Johnson SB Threeparameter Frechet Burr Frechet 100
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4. Our findings clearly show that the commonly used exponential growth of breast tumor will lead to incorrect decisions. 5. The commonly used standard lognormal proba bility distribution to characterize the behavior of the doubling time is not correct and will lead to wrong decisions. 6. One should be very careful in select ing one of the four volumes for a given situation because all are sensitive with respect to growth rate an age of the patients. 101
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Chapter 7 Statistical Modeling of Lung Cancer Mortality Time 7.1 Background and Data Lung cancer is a disease of uncontrolled cell growth in tissues of the lung and one of the deadliest common cancers in both men and women. Annually, 1.3 million deaths are caused by lung cancer wo rldwide. It is more common in older adults than in people under age 45. It is k nown that cigarette smoking is the leading cause of lung cancer, which means the risk of getting lung cancer is strongly associated with the number of cigarettes smoked per day and the time when one starts and quits smoking. Se condhand smoke contributes to lung cancer as well and there is a chance t hat people who have never smoked will get lung cancer. The data that were first collected in 1982 and the mortality followup in the dataset is complete through 2006. It encompasses 1.2 million subjects in 50 states. Only data fr om those who got lung cancer are included in this study, whether from smoking or nonsmoking. For exsmokers the total number of lung cancer patients is 5,316, of which 1,523 are females and 3,793 are males. For 102
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nonsmokers, the total number of lung cancer patients is 2,010, of which 1,386 are females and 624 are males. Although there are many ot her causes associated with lung cancer such as air pollution, radon gas, asbestos, family histor y of lung cancer, radiation therapy to the lungs, and exposure to cancercausing c hemicals, we confined our interest in smoking only due to the lack of data pertain ing to these other causes. The four variables of interest are the number of cigarettes per day (CPD), the age at which an individual started smoking ( ), the age at which an individual quit smoking ( ), smoking duration (in years),stqtqtts (DUR), and mortality time ( ). The following diagram gives a clearer vi ew of what the data looks lik e. mt Figure 7.1. Lung Cancer Data The objective of this study is to addre ss the following questions related to some of the most important entities in lung cancer: cigare ttes per day (CPD), time the patient started smoking ( ), time the patient quit smoking ( ), duration of stqt 103
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smoking which is defined as the diffe rence between the two above mentioned times (DUR), and, most importa ntly, the mortality time ( ): mt(1) What is the probabilistic nature of mortality time in exsmoker lung cancer patients and nonsmoker lung cancer patient s, for female, male, and the totality of female and male patients? (2) Is there significant difference of mortality time between exsmoker and nonsmoker patients? (3) For exsmokers, are there any differ ences with respect to the key variables such as mortality time, CPD, and durat ion of smoking between female and male patients? (4) For nonsmokers, can we notice a differ ence in mortality time between female and male patients? (5) Can we accurately predict mortalit y time given information on CPD, starting time and quitting time for a specific lung cancer patient who smokes? 7.2 Results of Parametric Analysis Before modeling mortality time as a function of CPD, DUR, , basic parametric analys is should be performed to understand its probabilistic behavior. More than 40 different classical distri butions are fit to the data and three goodnessoffit tests, KolmogorovSmirnov AndersonDarling and ChiSquare are conducted for the mortality time of lung cancer patients for female exstqt 104
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smokers, male exsmokers, all exsmo kers, female nonsmokers, male nonsmokers, all nonsmokers, respectively. T he parameters of the three distributions ranked the highest by goodnessoffit are listed and the 90% and 95% confidence intervals are constructed. T he results appear in the following tables where the first table shows the mean and va riance of the best fitting distribution and Table 7.2 shows the 90% and 95% confi dence bands of the true mean of the estimated distributions. As can be seen from the tables, the best fitting distribution is always Johnson SB followed by Beta distribution and threeparameter Weibull distribution. With this finding, we can find the mean and vari ance and construct the 90% and 95% confidence intervals for mortality time. An interesting thing worth noting is that no matter which distribution is chosen, Be ta, Johnson SB, or threeparameter Weibull, their 90% and 95% confidence in tervals are very close. Although Johnson SB appears to be the best fit for both female and male exsmokers and theoretically a likelihood ratio test coul d be applied to test the difference of means of mortality time in these two groups, the parametric comparison is not used here due to the extremely complicated calculation. Furthe rmore, it appears that there are no signific ant differences between the means and variances of mortality times for females and males. However, it is observed that exsmoker lung cancer patients have decreased mo rtality compared to nonsmoker lung cancer patients. These parametric results lead us to co mpare the key variables in the different groups, between female and males, or betw een nonsmokers and exsmokers using nonparametri c methods as described next. 105
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Table 7.1 Mean and Standard Deviat ion of Fitted Distributions Johnson SB Beta Three parameter Weibulll Female exsmokers NA 73.995 (8.9577) 74.007 (8.9365) Male exsmokers NA 74.543 (8.1875) 74.542 (8.2119) Exsmokers NA 74.384 (8.4155) 74.387 (8.428) Female nonsmokers NA 76.117 (10.213) 76.148 (10.165) Male nonsmokers NA 76.011 (9.6368) 76.015 (9.6551) Nonsmokers NA 76.085 (10.041) 76.103 (10.022) 106
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Table 7.2 Confidence In terval of the True Mean Johnson SB Beta Three parameter Weibulll Female exsmokers (59.9, 87.622) (55.419, 90.07) (58.586, 88.016) (55.364, 90.327) (58.456, 87.916) (55.371, 90.168) Male exsmokers (60.527, 87.493) (57.827, 89.55) (60.557, 87.52) (57.849, 89.591) (60.304, 87.386) (57.519, 89.482) Exsmokers (59.9, 87.622) (57.061, 89.701) (59.98, 87.659) (57.057, 89.85) (59.751, 87.541) (56.871, 89.68) Female nonsmokers (58.145, 91.777) (54.682, 93.933) (58.304, 91.886) (54.794, 94.142) (58.277, 91.742) (54.582, 94.205) Male nonsmokers (58.888, 90.419) (55.014, 92.541) (58.87, 90.391) (55.045, 92.434) (58.671, 90.298) (54.727, 92.425) Nonsmokers (58.367, 91.373) (54.761, 93.541) (58.461, 91.428) (54.811, 93.643) (58.354, 91.302) (54.567, 93.657) 107
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7.3 Results of Nonparametric Comparison After finding the mortality time for both exsmokers and nonsmokers, the next question is whether there is significant di fference of mortality time between exsmokers and nonsmokers, between fema le and male groups. We are also interested in the impact of the number of cigarettes smoked per day and duration of smoking on female and male smokers (for exsmokers only since they are all zeros for nonsmokers). The Wilcoxon Rank Sum two sample test by Wilcoxin (1945) was performed to detect location differences. The results are shown in Table 3. For all these tests of hypothesis we first set the null hypothesis to be twosided, if pvalue is large enough; we fail to reject the null hypothesis. However, if pvalue is sm all which suggests the rejection of the null hypothesis, we proceed to test the onesided hypothesis. Table 7.3 Wilcoxon TwoSample Test Result oH )( exmt )( nonmt ) ( exfemalemt = )( exmalemt ) ( nonfemalemt = )( nonmalemt female maleDPC DPC female maleRUD RUD pvalue 0.0018 0.1180 0.8106 <0.0001 0.0001 Conclusio n Reject Accept Accept Reject Reject 108
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(1) Mortality time between exsmokers and nonsmokers Mortality time of exsmokers and nonsmokers are compared using the Wilcoxon twosample test. Under hypothesis that )ker ( ssmoexmt )ker ( ssmononmt, the pvalue is 0.0018. Thus, using a significance level of 0.05, we reject the null hypothesis and conclude that nonsmoker lung cancer patients have longer mo rtality time than that of exsmokers. (2) ExSmokers mortality ti me between female and male There is no significant difference betwe en the female and male smokers with respect to the death time fr om lung cancer. For twosided hypothesis, the pvalue is 0.1180 and the pvalue for onesided hypot hesis is 0.0590 which is still higher than 0.05. Thus, using a significance leve l of 0.05, death time of female exsmokers is not significantly different from that of male exs mokers (p = 0.1180). (3) NonSmokers mortality ti me between female and male As can be seen from the twosided pvalue 0.8106 and onesided pvalue of 0.4053, there is insufficient evidence to conclude that there is a difference between female and male nonsmoker lung c ancer patients. Thus, no difference of mortality time can be found between fe male and male lung cancer patients, both in exsmokers and nonsmokers, which is consistent wit h the conclusion from parametric analysis. 109
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(4) Exsmokers CPD As can be seen from the pvalue, whic h is less than 0.0001 un der the hypothesis that male femaleCPDCPD there is strong evidence that males tend to have more cigarettes per day than females. (5) Exsmokers DUR Similarly, the pvalue of 0.0001 under null hypothesis that male femaleDURDUR suggests that smoking duration for male smokers exceeds the smoking duration of female smokers. In summarizing the above analyses, the following conclusions are obtained: (1) There is no significant difference in mean mortality time for females and males for both exsmokers and nonsmoker s. Exsmokers tend to have a shorter mortality time than nonsmokers. (2) For CPD, mean CPD of males is larger than that of females. (3) For DUR, males have longer dur ation of smoking than females. 7.4 Results of Modeling of mortality time After finding the probabilistic behavior of mortality time and comparison of key entities with respect to race and smoking status, we proceed to investigate the relation between mortality time and other attributable variables such as CPD, 110
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time an individual started smoking ( ), and time an individual quit smoking ( ), where multiple regression models is mos t commonly used tool. First, for the female exsmokers, multiple regression models were run and the backward selection method is used to eliminate any variables that do not significantly contribute. However, after multiple regr ession is applied using mortality time as the response variable and , and the secondorder interaction between them as well as t he quadratic terms, the Rsquare (0.2249) of the full model is pretty small which indicates multiple regression model is not a good choice here. The same procedur e was appl ied to male exsmokers, where the Rsquare was only 0.1301. ststqtCPDqtAlthough multiple regression models do not perform well, they give us some guidance on which variables are not im portant and can be eliminated in the modeling process later. We then proceeded to utilize the survival regression model, also called the accelerated failu re time (AFT) model, which assumes certain distribution of the response variables. (1) AFT model When covariates are considered, we assume that the relapse time has an explicit relationship with the covariates. Furt hermore, when a parametric model is considered, we assume that the rel apse time follows a given theoretical probability distribution and has an explicit relationship with the covariates. Females 111
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Survival regression models were run using statistical software including exponential, generalized gamma, loglogistic lognormal, logistic, normal, and Weibull distributions. Their log likelih oods were: 1532, 1215, 1189, 1194, 5326, 5309, 1185. Thus, the generalized gamma was determined to prove the best fit and backward elimination was used to eliminate the unimportant variables. In the final model, the variables left are CPD, interaction between and interaction between CPD and and quadratic terms of CPD and ststqtqtqtAll terms in the model are significant and they are ranked acc ording to their significance. The quadratic term of quitting time ranks first followed by CPD, starting time, interaction between star ting time and quitting time, quadratic term of CPD, and interaction between CPD and quitting time. The following percentage plot Figure 7. 2 is obtained for the final model. After the estimations of th e parameters in the model ar e obtained, the value of log(T) can be predicted by plugging the parameters into the equation, and thus mortality time T can be calculated by simply taking natural exponentials. The mean and standard deviation of the difference between predicted mortality time and observed mortality time are 0. 1378148 and 7.911363, respectively. However, the mean and variance of the difference between predicted log(T) and observed log(T) (residual) are only 0.008175027 and 0.1108183, respectively. Figure 7.3 shows the survival curves cons tructed by predicted mortality time and observed mortality time. 112
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Figure 7.2 Percentage Plot of Female ExSmokers 113
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02040608010 0 0.00.20.40.60.81.0 agesurvival probability 02040608010 0 0.00.20.40.60.81.0 agesurvival probability Observed: Pred icted: Figure 7.3 Predicted Survival Curve of Female Smokers After elimination of the insignificant vari ables, all the v ariables left in the models are significant and the loglikelihood is not much changed. As can be observed from the Figure 7.2, all t he data falls within the 95% confidence interval of the estimated percentage except in the left ta il which suggests the model is fairly accurate. Males The same procedure is followed for ma le exsmoker lung cancer patients. Survival regression models were run in cluding exponential, gamma, loglogistic, 114
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lognormal, logistic, normal, and Weibull. A nd their log likelihoods are as follows: 3814, 3209, 3128, 3160, 13152, 13093, 3121. Thus, the three parameter gamma is chosen to be the best fitting di stribution and backward elimination is used to eliminate interactions between CPD and and and the quadratic term of In the final model, the variables left are CPD, , interaction between CPD and and quadratic terms of CPD and stst tqtststqtqtqAll the terms are significant, and quadr atic term of quitting time ranks first followed by quitting time, CPD, starti ng time, interaction between CPD and quitting time, and quadratic term of CPD comes last. Figure 7.4 Percentage Plot of Male ExSmokers 115
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Similarly, after plugging the estimat ed parameters into the model and obtaining the value of log(T) mortality time T can be easily calculated by taking natural exponentials. The mean and standard devia tion of the difference between predicted mortality time and observ ed mortality time are 0.1439845 and 7.651358, respectively. However, since the model is constructed using log(T) as the response variable, the mean and variance of the difference between predicted log(T) and observed log( T) are only 0.007539421 and 0.1054347, respectively, which indicates the predict ive power of the model. Figure 5 below shows the survival curves constructed by predicted mortality time and observed mortality time. 02040608010 0 0.00.20.40.60.81.0 agesurvival probability 02040608010 0 0.00.20.40.60.81.0 agesurvival probability Observed: Predicted: Figure 7.5 Predicted Survival Curve of Male Smokers 116
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As can be observed from Fi gure 7.4, the percentage calc ulated from real data falls well within the 95% confidence inte rval constructed from the mode. This suggests the model is fairly accurate. 7.5 Discussion The current chapter performs parametric and nonparametric analysis to address some very important questions concerning lung cancer utilizing real lung cancer data: What is the probabilistic nature of mortality time in exsmoker lung cancer patients and nonsmoker lung cancer patient s, for female, male, and the totality of female and male patients? Is there si gnificant difference of mortality time between exsmoker and nonsmoker patient s? For exsmokers, are there any differences with respect to the key variabl es such as mortality time, CPD, and duration of smoking between female and ma le patients? For nonsmokers, can we notice a difference in mortality time between female and male patients? Can we accurately predict mortality time gi ven information on CPD, starting time and quitting time for a specific lung cancer patient who smokes? Thus best fitting probability distributions are identified and their paramet ers are estimated. Mean mortality times are compared between nonsmokers and exsmokers, female nonsmokers and male nonsmokers, and female exsmokers and male nonsmokers. Important entities related to lung cancer mortality time, such as cigarettes per day (CPD), and durati on of smoking ( DUR), are compared between female and male exsmoker lung c ancer patients. Finally, a model is 117
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developed to predict the mortality time of exsmokers with a high degree of accuracy. By using parametric analysis, distributions of mortality time for both female and male exsmokers and nonsmokers are found. Ninety percent and 95% confidence intervals are constructed which provide basic information on the probabilistic behavior of mortality time. Using nonparametric methods, we found that there is no significant difference in mean mortality time for females and males for both exsmokers and nonsmoker s. Exsmokers tend to have a shorter mortality time than nonsm okers; mean CPD of males is larger than that of females; males have longer duration of smoking than females. Lastly, an accelerated failure time model is constr ucted for female and male lung cancer patients, respectively, so that given information on cigarettes per day, time started smoking, and time quit smoking of a specific smoker, mortality time can be predicted. 118
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Chapter 8 Conclusion and Future Research 8.1 Conclusions We applied various statistical approaches to modeling and predicting the survival time, relapse time of breast cancer patients, mortality time of lung cancer patients. We also utilized parametric and nonparamet ric comparisons including decision tree techniques to investigate the effect iveness of breast cancer treatments and showed the combined treatment of Tamoxifen and radiation is not always more effective than Tamoxifen only and different treatment should be given to patients with heterogeneous prognostics factors. Markov Chain also confirmed that different treatment should be given based on the stages of brea st caner patients and the transition probability are calculat ed between stages of patients with different treatments. We also used parametric analysis to s how the sensitivity of breast tumor doubling time with different volume and gr owth assumptions. The results showed the probabilistic behavior of doubling time is very sensitive to the choice of volume and growth assumptions of tumors and lognormal probabilistic distribution is not the best choice to characterize tumor doubling time. 119
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Nonparametric comparisons are conducted to analyze the mortality time between different genders, smoking status and mortality time is modeled for prediction purpose. 8.2 Future Research Future validation of the models may be conducted using cross validation or by using new data. Other datasets such as SEER could provide more relevant information on breast cancer such as sur gery, chemo theory, number of lymph nodes involved, ect, thus providing more compressive understanding of breast cancer. With the increased number of variables and need to identified attributable variables, considering the fact that accelerated failure model is extensively used in survival analysis and current statistical software does not provide variable selection in the accelerated failure ti me regression model, statistical package should be developed to satisfy such need. Currently a stepwise selection SAS macro based on pvalue in accelerated failu re model SAS procedure as shown in Figure 8.1 has been written and will be implement ed the analysis in the future. Stepwise Selection Algorithm: 1. Run univariate regression with each variable; select the one with the lowest pvalue into the initial model 2. Run the existing model, if any term in the model has pvalue > exit tolerance, remove the variable with largest pvalue and go to 3. 120
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3. Run the model with each remaining variable added to the existing model one at a time, if any term in the model has pvalue < entrance tolerance, add the one with smallest pval ue and repeat 2 and 3. 4. Stop until all the terms in the model have pvalue < ex it tolerance, and all the remaining variables have pvalue > entranc e tolerance if added to the existing model one at a time. That is, no variabl e can be eliminated from the existing model, and no variable needs to be added to the existing model. %SurvivalSelection %ScanVar %UniFit %Selection Loop Yes No Yes No PROC LIFEREG: fit univariate model with each covariate. Create data set in_model with the covariate with lowest pvalue, and out_model with the rest covariates PROC LIFEREG: fit model with covariates in in_model Identify max pvalue Is max pvalue > &PEXIT? Remove variable from in_model add variable to out_model. PROC LIFEREG: fit model with covariates in in_model plus one variable at a time in out_model Identify min pvalue of out_model variables Is min pvalue < &PENTRANCE? Final Model Remove variable from out_mode, Add variable to in_model Figure 8.1 Stepwise Variable Selection Macro Last but not least, the methods used in t he current study could be implemented in the study of other types of cancer in providing important information on 121
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treatment of cancer pati ents, transition of cancer stages and prediction of reoccurrence and survival time. 122
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References A. W. Fyles, D.R. McCready, et al. ( 2004) Tamoxifen with or without breast irradiation in women 50 years of age or older with early breast cancer, New England Journal of M edicine 351, pp. 963970. A.A. Markov. (1971) "Extens ion of the limit theorems of probability theory to a sum of variables connected in a chain". reprinted in Appendix B of: R. Howard. Dynamic Probabilistic Systems, volume 1: Markov Chains. John Wiley and Sons. Akaike H. (1974) A new look as the stat istical model identification. IEEE Trans Automatic Control, 1974, 19: 71623. Anderson, T. W.; Darling, D. A. (1952) "Asymptotic theory of certain "goodnessoffit" criteria based on stochastic processes". Annals of Mathematical Statistics, 23: 193.. Bacchetti, P. and Segal M. R. ( 1995): Survival trees with timedependentcovariates: application to estimating changes in the incubation period of AIDS Lifetime Data Analysis Vol. 1, number1. Boag JW. (1949) Maximum likelihood esti mates of the proportion of patients cured by cancer therapy. J Roy Stat Soc B; 11: 1544. Breiman, L., Friedman, J., Olshen, R., and Stone, C. (1984): Classification and Regression Trees, New York; Chapman and Hall Breiman, Leo (2001): Random Forests, Machine learning, 45 (1): 5. Bryant, A; Cerfolio RJ. (2007) Differences in epidemiology, histology, and survival between cigarette smokers and neversmokers who develop nonsmall cell lung cancer ". Chest 132 (1): 198. Chernoff, H. ; Lehmann E.L. (1954) "The use of maximum likelihood estimates in 2 tests for goodnessoffit". The Annals of Mathematical Statistics 25: 579. ChinShang Li, Jeremy M.G. Taylor (2002) A semiparametric accelerated failure time cure model. Statistics in Medicine; 21: 32353247. Claude Shannon and Warren Weaver( 1949) publication model of communication 123
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Davis, R. and Anderson, J. (1989): Exponential surviv al trees, Statistics in Medicine 8, pp 947962. F. Gao, A. K. Manatunga, and S. Chen (2004), Ident ification of prognostic factors with multivariate survival dat a, Computational St atistics and Data Analysis 45, pp. 813824 Fabien Corbiere, Pierre Joly (2007) A SAS macro for parametric and semiparametric mixture models. Co mputer Methods and Programs in Biomedicine; 85(2): 17380. Farewell, V.T. (1982) The use of mixture models for the analysis of survival data with longterm survivors. Biometrics; 38: 10411046. Gordon, L. and Olshen, R. A. (1985): Treestructured survival analysis. Cancer Treatment Repor ts 69, 10651069. Green L. (2009) Age Depen dent Screening, SIAM Conference Mathematics for Industry: Challenges and Frontiers, San Francisco, California. Harrington, D. P. and Fleming, T. R. (1982): A class of rank test procedures for censored survival data. Biometrika 69, 553566. Heuser, L. et. al. (197 9). Growth Rates of Pr imary Breast Cancers. Cancer 43: 18881894. Jones, D.R, Powles, R.L., Machin, D. and Sylvester, R.J.(1981) On estimating the proportion of cured patients in clin ical studies. BiometriePraximetrie,; 21: 111. Kaplan, E.L.; Meier, Paul. (1958): Nonpar ametric estimation from incomplete observations, J. Am. St at. Assoc. 53, 457481. Lebalanc, M.; Crowlry, L. (1992): Relative risk trees for censored survival data, Biometrics. v48. 411425. LeBlanc, M., Crowley, J. (1993). Survival trees by goodness of split. Journal of the American Statistica l Association 88, 457 Loh, W. Y. and Shih, Y. S. (1997): Split selection methods for classification trees. Statistica Sinica, Vo l. 7, p. 815 840. M.T. Uddin, M.N. Islam and Q.I.U. Ibrahi m (2006), An analytical approach on cure rate estimation based on unc ensored data. Journal of Applied Sciences; 6(3): 548552. 124
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125 MAGIDSON, J. (1993): The use of the new ordinal algorithm in CHAID to targetprofitable segments, The Journal of Database Marketing, 1, 29. Mann, H. B. & Whitney, D. R. (1947) "On a te st of whether one of two random variables is stochastically larger than the other". Annals of Mathematical Statistics, 18 50. N.A Ibrahim, et al. (2008): Decision tree fo r competing risks survival probability in breast cancer study, International Jour nal of Biomedical Sciences Volume 3 Number 1. Orbe J, Ferreira E, NunezAnton V. ( 2002) Comparing proportional hazards and accelerated failure time models for survival analysis. Statist med; 21: 3493510. Peer P. G. M. et al. (1993). Age Dependent Growth Rate of Primary Breast Cancer. Cancer 71: 354751. Plackett, R.L.(1983) Karl Pearson and the ChiSquared Test ". International Statistical Review 51 (1): 59. Quinlan, J. R. (1986): Induc tion of Decision Trees. Ma chine. Learning 1, 1, 81106. Segal M. R. (1988): Regression trees for censored data, Biometrics 44, pp.3547. Thun, MJ; Hannan LM, AdamsCampbell LL et al. (2008), "Lung Cancer Occurrence in NeverSmokers: An An alysis of 13 Cohorts and 22 Cancer Registry Studies". PLoS Medicine 5 (9): e185. Wilcoxon, F. (1945), "I ndividual comparisons by ranking methods". Biometrics Bulletin, 1, 80. Yamaguchi K. (1992), Accelerated fa iluretime regression model with a regression model of surviving fraction: an application to the analysis of permanent employment in Japan. Journal of the Amer ican Statistical Association; 83:222230. Yingwei Peng, Keith B.G. Dear and J.W. Denham (1998), A generalized F mixture model for cure rate estimation. Statistics in Medicine; 17: 813830.
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About the Author Chunling Cong got her undergraduate degr ee at Nanjing University of Technology in China and came to the Un ited States for higher education at University of South Flor ida at fall, 2005. She go t her master degree in Mathematics at the end of 2006 and c ontinued pursuing her Ph. D degree with a concentration in Statistics. She got a summ er internship at Statistical Evaluation Center in American Cancer Society in 2009. Beside Statistical Analysis, she developed great interest in actuarial science and worked in Travelers Companies, Inc as a summer intern which led to a permanent position as a senior consultant in Claim Research Department in 2010.
