OBJECTIVES:

• Determine whether nutritional supplementation with soy protein isolate, vitamin E, and selenium can delay the time to development of invasive prostate cancer (disease-free survival) in patients with high-grade prostatic intraepithelial neoplasia.
• Determine the effect of this supplementation on intermediate endpoints that may reflect a lessened risk of invasive prostate cancer (e.g., serum PSA levels, hormone levels, lycopene, malondialdehyde, vitamin E, and reduced thiol groups) in these patients.
• Determine the safety of this supplementation in these patients.

OUTLINE: This is a randomized, double-blind, multicenter study. Patients are stratified according to participating center. Patients are randomized to 1 of 2 treatment arms.

• Arm I: Patients receive oral vitamin E, oral selenium, and oral soy protein isolate twice daily.
• Arm II: Patients receive oral placebo twice daily. In both arms, treatment continues for 3 years in the absence of invasive prostate cancer (demonstrated on biopsy) or unacceptable toxicity.

Patients are followed every 3 months for 1 year and then every 6 months for 2 years.

PROJECTED ACCRUAL: A total of 306 patients (153 per treatment arm) will be accrued for this study within 6 years.

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