Inclusion Criteria

DISEASE CHARACTERISTICS: Histologically confirmed stage B, C, or D adenocarcinoma of the
prostate not amenable to surgery

PATIENT CHARACTERISTICS: Age: 40 and over Performance status: ECOG 0-2 Life expectancy: At
least 6 months Hematopoietic: WBC at least 3,500/mm3 Platelet count at least 100,000/mm3
Hepatic: Bilirubin no greater than 2.0 mg/dL Transaminases less than 4 times upper limit
of normal Renal: Creatinine less than 2.0 mg/dL Cardiovascular: No New York Heart
Association class III or IV heart disease Other: No significant abnormalities of internal
organs, neurologic status, or biochemical levels No history of seizures No concurrent
serious illness No acute infection requiring antibiotic therapy except chronic urinary
tract infection No other prior or concurrent malignancy within the past 2 years except
nonmelanoma carcinoma of the skin No history of substance abuse or addiction No alcohol
intake greater than 2 drinks/day or 14 drinks/week No diet containing more than 20 mg of
genistein/day No known soy intolerance No prior breast cancer

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: Not specified
Endocrine therapy: At least 3 months since prior hormonal therapy OR No concurrent
estrogen Other concurrent hormonal therapy allowed if stable regimen for more than 3
months Radiotherapy: At least 4 weeks since prior radiotherapy and recovered Surgery: See
Disease Characteristics At least 3 weeks since prior surgery and recovered Other: At least
6 weeks since prior antibiotics No concurrent genotoxicity therapy