Vitamin E, Selenium, and Soy Protein in Preventing Cancer in Patients With High-Grade Prostate Neoplasia

DISEASE CHARACTERISTICS: * Histologically confirmed high-grade prostatic intraepithelial neoplasia (HGPIN) * No evidence of invasive prostate cancer by at least 2 biopsies within the past 18 months * At least 1 biopsy must show evidence of HGPIN within the past 6 months * No prior invasive prostate cancer PATIENT CHARACTERISTICS: Age * Not specified Performance status * Not specified Life expectancy * More than 5 years Hematopoietic * Platelet count at least 75,000/mm\^3 * No coagulopathies Hepatic * Bilirubin no greater than 2 times upper limit of normal (ULN) * PT (INR) no greater than 1.5 times ULN * PTT no greater than 1.5 times ULN * No hepatic insufficiencies Renal * Creatinine no greater than 2 times ULN * No renal insufficiencies Other * No prior nonmelanoma skin cancer (e.g., squamous cell or basal cell carcinoma) * No other malignancy within the past 5 years except superficial bladder cancer * No known bowel malabsorption * No dietary behavior (e.g., morbid obesity or eating disorders) that would limit adherence to study therapy * No major illness, including psychiatric illness, that would preclude study compliance and follow-up PRIOR CONCURRENT THERAPY: Biologic therapy * Not specified Chemotherapy * Not specified Endocrine therapy * More than 3 months since prior androgen therapy * More than 3 months since prior hormonal therapy for benign prostatic hyperplasia (e.g., finasteride) * No concurrent finasteride * No concurrent androgen therapy Radiotherapy * More than 2 years since prior radiotherapy to the pelvic region Surgery * Not specified Other * More than 2 weeks since prior supplemental vitamin E or selenium * No other concurrent vitamin E (greater than 100 IU/day), selenium, or soy protein isolate (more than 2 servings/week) * No other concurrent treatment for high-grade prostatic intraepithelial neoplasia