• Oxidative DNA damage as measured by 5-hydroxymethyluridine level at 3 weeks [ Designated as safety issue: No ]
  
• Lipid oxidation as measured by 8-isoprostane level at 3 weeks [ Designated as safety issue: No ]
  

• Tumor size, grade, and extension at 3 weeks [ Designated as safety issue: No ]
  
• Prostate-specific antigen and prostatic intraepithelial neoplasia grade at 3 weeks [ Designated as safety issue: No ]
  
• Biomarkers of cell growth, differentiation, and apoptosis at 3 weeks [ Designated as safety issue: No ]
  
• Toxicity as measured by number and grade of adverse events at 3 weeks [ Designated as safety issue: Yes ]
  

OBJECTIVES:

• Compare blood/prostate biomarkers of oxidative stress and prostate cancer risk in patients with stage I or II adenocarcinoma of the prostate treated with 3 different dose levels of soy isoflavones before radical prostatectomy.
• Compare prostatic tissue biomarkers of proliferation and apoptosis in patients treated with these regimens.
• Determine the potential response, in terms of tumor and prostatic intraepithelial neoplasia grade and volume, extraprostatic extension, and serum prostate-specific antigen level, in patients treated with soy isoflavones and in those treated with placebo.
• Determine the safety of soy isoflavone supplementation in these patients.

OUTLINE: This is a randomized, double-blind, placebo-controlled, parallel-group study. Patients are stratified according to tumor stage (T1c vs T2). Patients are randomized to 1 of 4 treatment arms.

• Arm I (control group): Patients receive oral placebo once daily.
• Arm II: Patients receive oral soy isoflavones and oral placebo once daily.
• Arm III: Patients receive a higher dose of oral soy isoflavones and oral placebo once daily.
• Arm IV: Patients receive a higher dose (higher than arm III) of oral soy isoflavones once daily.

In all arms, treatment continues for 2-6 weeks (depending on the time from study entry to planned surgery) in the absence of unacceptable toxicity. All patients then undergo radical prostatectomy.

Patients are followed at 1 week.

PROJECTED ACCRUAL: A total of 100 patients (25 per treatment arm) will be accrued for this study within 12.5 months.

DISEASE CHARACTERISTICS:

• Histologically confirmed adenocarcinoma of the prostate

  • Stage T1c or T2
  • Disease confined to the prostate gland
• Planning to undergo radical prostatectomy within the next 3-4 weeks

PATIENT CHARACTERISTICS:

Age

• 18 and over

Performance status

• Not specified

Life expectancy

• Not specified

Hematopoietic

• Not specified

Hepatic

• ALT and AST less than 2 times upper limit of normal (ULN)
• Alkaline phosphatase less than 2 times ULN

Renal

• Not specified

Other

• Fertile patients must use effective barrier contraception
• Medically cleared for surgery
• No concurrent thyroid disease

PRIOR CONCURRENT THERAPY:

Biologic therapy

• No prior biological therapy for prostate cancer
• No concurrent biological agents

Chemotherapy

• No prior chemotherapy for prostate cancer
• No concurrent chemotherapy

Endocrine therapy

• No prior hormonal therapy for prostate cancer
• No concurrent thyroid hormone replacement medication
• No concurrent hormonal therapy

Radiotherapy

• Not specified

Surgery

• See Disease Characteristics

Other

• At least 3 months since prior high-dose nutritional supplements
• No concurrent regular use (more than once weekly) of soy products greater than 50 g of soy protein or 50 mg of soy isoflavone

• No concurrent high-dose nutritional supplements

  • Standard-dose single multivitamin tablet (e.g., Centrum™) allowed
• No concurrent herbs
• No concurrent soy foods
• No other concurrent isoflavone supplements
• No other concurrent antineoplastic agents