Purpose: We describe the complexities of the study design of the PCPT and how they influenced the end point chosen, trial implementation, analysis and interpretation of the results. Materials and Methods: Data from the PCPT are provided to evaluate and quantify the potential biases of this trial design. Results: Six potential sources of bias, including prostate specific antigen, digital rectal examination, prostate biopsy technique, study medication nonadherence and contamination, and transurethral prostate resection are presented. These biases resulted in the need for the end of study biopsy to evaluate the trial objectives. Conclusions: There were a large number of known and potential biases that worked for and against finasteride. Because of the trial design and inherent biases, it is imperative that interim biopsy results should be interpreted with caution. While the period prevalence end point that relied on an end of study biopsy was perhaps not the most clinically relevant, it was the only way to remove as much bias as possible and meet the study objective of determining if finasteride could decrease the risk of prostate cancer. The success of the PCPT depended on constant scrutiny by the Data and Safety Monitoring Committee to monitor these biases. The design and biopsy assumptions outlined at the inception of the trial were met, including adherence and contamination rates, the for-cause biopsy rate and the final percent of men with study end points.
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