Genistein in Treating Patients With Localized Prostate Cancer Who Are Planning to Undergo Radical Prostatectomy

DISEASE CHARACTERISTICS: * Diagnosis of localized prostate cancer * Diagnosed within the past 6 months * T1 or T2 disease * Gleason score 5-8 * Prostate-specific antigen no greater than 20 ng/mL * Radical prostatectomy planned PATIENT CHARACTERISTICS: Age * 18 and over Performance status * ECOG 0-1 Life expectancy * More than 2 years Hematopoietic * Hemoglobin greater than 9.0 g/dL * Platelet count greater than 100,000/mm\^3 * Absolute neutrophil count greater than 1,000/mm\^3 Hepatic * SGPT and SGOT less than 3 times normal * Bilirubin less than 3 mg/dL (less than 1.5 times normal) (patients with an elevated bilirubin due to a familial defect in bilirubin metabolism will be considered on an individual basis) Renal * Creatinine less than 2.0 mg/dL Cardiovascular * No venous thrombosis within the past year Other * Patients must use effective barrier contraception * No other medical condition that would preclude study therapy * No known soy intolerance PRIOR CONCURRENT THERAPY: Biologic therapy * Not specified Chemotherapy * Not specified Endocrine therapy * No concurrent hormonal therapy for prostate cancer Radiotherapy * Not specified Surgery * See Disease Characteristics Other * No concurrent soy supplements * No concurrent foods high in genistein * No concurrent active therapy for neoplastic disorders