A dietary supplement containing genistein, a soy extract, reduced prostate-specific antigen (PSA) levels by as much as 61% in a group of prostate cancer patients undergoing “watchful waiting” for their disease, say cancer researchers at the UC Davis Cancer Center. PSA is a blood marker for prostate cancer. An increase in PSA is a warning sign of prostate cancer. Watchful waiting is recommended for some men whose cancer is causing no symptoms, is expected to grow very slowly, and is small and contained within one area of the prostate.

In the study, 62 men with biopsy-proven prostate cancer and elevated PSA levels were given 5 grams a day of genistein for six months. Sixteen of the men were on watchful waiting for their disease. Of those men, 13 completed the study and eight saw a drop in their PSA level. The decreases in PSA ranged from 3% to 61%. The dietary supplement did not have the same effect in men who had undergone surgery, radiation or hormone therapy for their prostate cancer. In this group, almost all saw a rise in PSA levels.

“Patients on watchful waiting may do better due to grade of disease or distribution and concentration of genistein within the prostate,” the study authors suggest. “Further research is needed to determine this.”

Genistein is one of two compounds in soy that belong to a family of chemicals known as isoflavones. Isoflavones are phytoestrogens, plant-based chemicals that mimic the effects of estrogen in the body. Genistein concentrated polysaccharide has been widely used as a complementary therapy for various cancers in Japan, Korea and other parts of Asia.

University of California, Davis, May 1, 2003