OBJECTIVES: * Compare blood/prostate biomarkers of oxidative stress and prostate cancer risk in patients with stage I or II adenocarcinoma of the prostate treated with 3 different dose levels of soy isoflavones before radical prostatectomy. * Compare prostatic tissue biomarkers of proliferation and apoptosis in patients treated with these regimens. * Determine the potential response, in terms of tumor and prostatic intraepithelial neoplasia grade and volume, extraprostatic extension, and serum prostate-specific antigen level, in patients treated with soy isoflavones and in those treated with placebo. * Determine the safety of soy isoflavone supplementation in these patients. OUTLINE: This is a randomized, double-blind, placebo-controlled, parallel-group study. Patients are stratified according to tumor stage (T1c vs T2). Patients are randomized to 1 of 4 treatment arms. * Arm I (control group): Patients receive oral placebo once daily. * Arm II: Patients receive oral soy isoflavones and oral placebo once daily. * Arm III: Patients receive a higher dose of oral soy isoflavones and oral placebo once daily. * Arm IV: Patients receive a higher dose (higher than arm III) of oral soy isoflavones once daily. In all arms, treatment continues for 2-6 weeks (depending on the time from study entry to planned surgery) in the absence of unacceptable toxicity. All patients then undergo radical prostatectomy. Patients are followed at 1 week. PROJECTED ACCRUAL: A total of 100 patients (25 per treatment arm) will be accrued for this study within 12.5 months.
DISEASE CHARACTERISTICS: * Histologically confirmed adenocarcinoma of the prostate * Stage T1c or T2 * Disease confined to the prostate gland * Planning to undergo radical prostatectomy within the next 3-4 weeks PATIENT CHARACTERISTICS: Age * 18 and over Performance status * Not specified Life expectancy * Not specified Hematopoietic * Not specified Hepatic * ALT and AST less than 2 times upper limit of normal (ULN) * Alkaline phosphatase less than 2 times ULN Renal * Not specified Other * Fertile patients must use effective barrier contraception * Medically cleared for surgery * No concurrent thyroid disease PRIOR CONCURRENT THERAPY: Biologic therapy * No prior biological therapy for prostate cancer * No concurrent biological agents Chemotherapy * No prior chemotherapy for prostate cancer * No concurrent chemotherapy Endocrine therapy * No prior hormonal therapy for prostate cancer * No concurrent thyroid hormone replacement medication * No concurrent hormonal therapy Radiotherapy * Not specified Surgery * See Disease Characteristics Other * At least 3 months since prior high-dose nutritional supplements * No concurrent regular use (more than once weekly) of soy products greater than 50 g of soy protein or 50 mg of soy isoflavone * No concurrent high-dose nutritional supplements * Standard-dose single multivitamin tablet (e.g., Centrum™) allowed * No concurrent herbs * No concurrent soy foods * No other concurrent isoflavone supplements * No other concurrent antineoplastic agents
are designated in this study