RATIONALE: Dietary supplementation with soy may keep prostate cancer from growing in patients planning to undergo surgery.

PURPOSE: This randomized phase II trial is studying a soy supplement to see how well it works compared to a placebo in treating patients undergoing surgery for localized prostate cancer.

OBJECTIVES:

Primary

• Compare the effect of dietary supplementation with soy vs placebo on biomarkers of cell cycle regulation, proliferation, differentiation, apoptosis, and signaling pathways in patients with localized prostate cancer scheduled to undergo radical prostatectomy.

Secondary

• Compare the toxicity and side effects of these regimens in these patients.
• Compare the dietary patterns of these patients.

OUTLINE: This is a prospective, randomized study. Patients are randomized to 1 of 2 treatment arms.

• Arm I: Patients receive oral soy supplementation daily for 4 weeks.
• Arm II: Patients receive oral placebo supplementation daily for 4 weeks. Patients undergo radical prostatectomy within 21 days after completion of soy or placebo supplementation.

Blood and tissue samples are collected for biomarker analysis using immunohistochemistry.

DISEASE CHARACTERISTICS:

• Histologically confirmed adenocarcinoma of the prostate

  • Clinically localized disease

• Scheduled for radical prostatectomy

• No evidence of metastatic disease by bone scan or CT scan of the abdomen or pelvis

PATIENT CHARACTERISTICS:

• ECOG performance status 0-2
• No evidence of active nephrolithiasis
• No history of hypercalcemic syndrome

PRIOR CONCURRENT THERAPY:

• No prior treatment for prostate cancer, including radiotherapy, systemic chemotherapy, surgery, or investigational drugs
• No other concurrent dietary supplementation with soy, cholecalciferol (vitamin D), or fish oil