Soy Protein Supplement in Preventing Prostate Cancer in Patients With Elevated Prostate-Specific Antigen Levels

OBJECTIVES: * Compare the reduction in the rate of prostatic cellular proliferation in patients with an elevated PSA (5 to 10 ng/mL) and a negative biopsy for prostate cancer when treated with daily soy protein supplements vs placebo. * Compare the effect of these regimens on additional biomarkers of prostate cancer (PSA, high-grade prostate intraepithelial neoplasia, induction of apoptosis, sex steroid receptor expression, and loss of glutathione S-transferase-pi) in these patients. * Compare the effect of these regimens on quality of life, including urinary and sexual function, in these patients. OUTLINE: This is a randomized, double-blind, placebo-controlled, multicenter study. Patients are stratified according to race (Caucasian vs African American). After 2 weeks of daily oral placebo, patients are randomized to 1 of 2 arms. * Arm I: Patients receive oral soy protein supplement daily for 12 months. * Arm II: Patients receive oral placebo daily for 12 months. Quality of life is assessed at baseline and at 6 and 12 months. PROJECTED ACCRUAL: A total of 160 patients (80 per arm) will be accrued for this study within 12 months.