This article discusses the basic elements of chemoprevention trial designs using cohorts of men following radical prostatectomy who either have prostate-specific antigen (PSA) failure indicative of recurrence or are at high risk for recurrence (positive surgical margins, extracapsular extension, seminal vesicle invasion, positive lymph nodes, Gleason score of greater than or equal to 8, preoperative serum PSA less than 20 ng/mL). Two ongoing randomized, double-blind, placebo-controlled clinical trials with soy protein as intervention in these 2 populations are described. In the trial with men at high risk for recurrence, participants started intervention within 4 months after surgery and were followed for up to 2 years; primary endpoints were PSA failure rate and time-to-PSA failure. In the trial with men with PSA failure (PSA 0.1 to 2.0 ng/mL), participants received treatment for 8 months and the primary endpoint is rise in PSA over time. The strengths and limitations of these designs are discussed and interim experience using studies with soy protein as the intervention agent are summarized.
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