Soy Extract Reduces PSA Levels in Men with Untreated Prostate Cancer, UC Davis Study Shows

(CHICAGO) -- A dietary supplement containing genistein, a soy extract, reduced PSA levels by as much as 61 percent in a group of prostate cancer patients undergoing "watchful waiting" for their disease, UC Davis Cancer Center researchers reported at the 2003 meeting of the American Urological Association meeting here Wednesday morning. The dietary supplement did not have the same effect in men who had undergone surgery, radiation or hormone therapy for their prostate cancer.

"This study must be interpreted cautiously because the numbers of men enrolled are small," emphasized Ralph deVere White, professor and chair of urology at UC Davis School of Medicine and Medical Center and director of the UC Davis Cancer Center. "However, the findings do stimulate us to do a larger, placebo-controlled trial in patients who are on watchful waiting." 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 concentrated polysaccharide for six months. Sixteen of the men were on watchful waiting for their disease. The remaining 46 had undergone surgery, radiation or hormone therapy.

Of those 46 men, one had no change in his PSA level during the study; the rest all had increases in PSA.

Among the 16 men on watchful waiting, three stopped therapy due to diarrhea. Of the 13 who completed the study, eight saw a drop in their PSA level. The decreases in PSA ranged from 3 percent to 61 percent.

Five of the 13 watchful waiting patients who completed the study, or 38 percent, had increased PSA levels over the course of the study, compared with 98 percent of the men with treated prostate cancer.

"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.

PSA, for prostate-specific antigen, is a blood marker for prostate cancer. An increase in PSA is a warning sign of prostate cancer. Elevated PSA levels in men who have been treated for prostate cancer may signal a recurrence or progression of the disease.

The UC Davis study was supported by Amino Up Chemical Co. of Sapporo, Japan, a genistein supplement manufacturer.

UC Davis Cancer Center, the only National Cancer Institute-designated center between San Francisco and Portland, Ore., is a program of the UC Davis School of Medicine and Medical Center.

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