OBJECTIVES:
* Determine the effect of soy protein isolate (isoflavones) and radiotherapy on the modulation of biomarkers in patients with localized prostate cancer.
* Determine the toxicity of this regimen in these patients.
* Determine the effect of this regimen on the quality of life of these patients.
OUTLINE: This is a randomized, placebo-controlled study. Patients are randomized to 1 of 2 treatment arms.
* Arm I: Patients receive oral soy protein isolate (isoflavones) twice daily for 6 months in the absence of disease progression or unacceptable toxicity.
* Arm II: Patients receive an oral placebo twice daily for 6 months in the absence of disease progression or unacceptable toxicity.
In both arms, patients also undergo radiotherapy while receiving isoflavones or placebo.
Quality of life is assessed periodically.
PROJECTED ACCRUAL: A total of 70 patients will be accrued for this study.
