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

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

RATIONALE: Soy protein supplement may prevent or delay the development of prostate cancer in patients who have elevated prostate-specific antigen (PSA) levels. PURPOSE: Randomized phase II trial to determine the effectiveness of soy protein supplement in preventing prostate cancer in patients who have elevated PSA 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.

DISEASE CHARACTERISTICS: Histologically confirmed absence of prostate cancer Atypical adenomatous hyperplasia or prostatic intraepithelial neoplasia (high-grade or low-grade) allowed Abnormal baseline transrectal ultrasound and digital rectal exam allowed Biopsy may be before or after study entry, but must be within the past 90 days PSA 5-10 ng/mL PATIENT CHARACTERISTICS: Age: 50 and over Performance status: ECOG 0-2 Life expectancy: Not specified Hematopoietic: Not specified Hepatic: Not specified Renal: Not specified Other: No known allergy to soy protein or milk protein No invasive cancer within the past 5 years except non-melanoma skin cancer PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: Not specified Endocrine therapy: No prior hormonal therapy No prior finasteride No concurrent hormonal therapy No concurrent finasteride Radiotherapy: Not specified Surgery: At least 6 months since prior transurethral resection of the prostate No prior orchiectomy No concurrent orchiectomy Other: No other concurrent soy products