Statistical Design Issues and Other Practical Considerations for Conducting Phase III Prostate Cancer Prevention Trials

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Abstract
We briefly describe the purpose of phase II studies as a source of preliminary data for phase III prevention trials, and address statistical and other practical considerations for phase III prostate cancer prevention trials. Objectives of 2 types of phase II studies and general criteria for validating surrogate end points are described, and statistical considerations needed for planning a phase III prevention trial are explained, including selection of an appropriate study population and end point, the corresponding expected event rate, estimates of loss to followup, and death and compliance rates. If a preventive agent has an impact on the ability to detect prostate cancer, additional study design considerations are then made. Other practical issues are addressed, including collection of biological materials for correlative studies, assessment of quality of life measures and the addition of ancillary studies that may include the collection of additional end points unrelated to prostate cancer. The Southwest Oncology Group is coordinating 2 recently reported phase III prostate cancer prevention trials. The Prostate Cancer Prevention Trial final results of 18,882 men randomized to either finasteride or placebo, and the Selenium and Vitamin E Cancer Prevention Trial has accrued more than half of its goal of 32,400 men. These studies are used to illustrate some statistical design features. The aforementioned trials provide valuable lessons in the successful design and conduct of phase III prostate cancer prevention trials.