Soy Isoflavones in Treating Patients With Recurrent Prostate Cancer or Rising Prostate-Specific Antigen

OBJECTIVES: I. To precisely quantify the absorption, serum concentrations over time, and excretion patterns of soy isoflavones and metabolites in men consuming the two bread products to define relationships between dietary intake, isoflavone metabolism and the biological outcomes. II. To describe the safety as well as incidence and severity of toxicity in men consuming the control soy bread or beta-glucosidase-enriched soy bread. III. To see if consumption of beta-glucosidase-enriched soy bread compared to control soy bread has a greater effect on blood hormonal patterns and biomarkers that favor anti-prostate cancer activity. IV. To see if beta-glucosidase-enriched soy bread compared to control soy bread improves hormonal patterns (lower insulin like growth factor-I, increased insulin like growth factor binding protein 3, lower androgens), reduce prostate specific antigen velocity, and lower circulating vascular endothelial growth factor concentrations. OUTLINE: Patients are randomized to 1 of 2 treatment arms (closed to accrual as of 02/14/2011). ARM I: Patients consume 2 slices of soy bread daily for 8 weeks. ARM II: Patients consume 2 slices of soy almond bread daily for 8 weeks. After a 2 week washout period, patients crossover to the alternate treatment arm.