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