SoyCaP: Soy and Prostate Cancer Prevention

Abstract

Abstract : The main objective of this project is to evaluate the effects of soy phytoestrogens on reproductive hormones and prostate tissue markers of cell proliferation and androgen action in men at high risk of prostate cancer. The hypothesis is that alteration of endogenous hormones is a mechanism by which soy phytoestrogens prevent prostate cancer. A randomized parallel arm study is being performed, in which 58 men at high risk of prostate cancer were randomized to receive one of three dietary supplements for six months: 1) soy protein isolate containing isoflavones; 2) isoflavone-poor soy powder; or 3) isoflavone-free milk powder. Urine and blood is collected at 0, 3 and 6 mo, for evaluation of serum hormones and prostate specific antigen, as well as urinary estrogen and phytoestrogen metabolites. At 0 and 12 mo, prostate biopsies aperformed to evaluate prostate tissue expression of apoptosis (Bax, Bcl-2), proliferation (PCNA), and androgen receptor density. We found isoflavone-rich soy protein isolate suppressed androgen receptor density, increased urinary estrogen excretion and increased the 2:16-OH estrone ratio in the urine. We also observed a trend toward a lower rate of prostate cancer in the men in the soy groups compared to the men in the milk group