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Soy Extract Shows Promise in Prostate Cancer Fight

Genistein checked the cancer in mice and lab studies, now being tested in humans

FRIDAY, June 8, 2001 (HealthDayNews) -- The soy extract genistein could become another tool in the fight against prostate cancer if tests on humans are as successful as new animal and laboratory studies, doctors say.

"The hope that genistein would be a cure by itself would not be reasonable, but it may work in conjunction with radiation and chemotherapy," says Dr. Ralph deVere White.

White is director of the Cancer Center at the University of California at Davis, where animal and lab studies of genistein found a reduction in prostate-cancer growth.

White presented the results of the studies at the recent annual meeting of the American Urological Association in Anaheim, Calif.

In White's animal study, mice that had been bred to develop prostate cancer were fed large doses of genistein and their tumors were reduced. Genistein is one of two soy compounds called isoflavones, which are plant-based chemicals that mimic the effects of estrogen in the body.

In the related lab study, genistein was added to a culture of prostate cancer cells and it spurred the production of a gene called p21, which inhibits the growth of a protein that helps cancer grow. The prostate cancer cells then died.

Prostate cancer is the most commonly diagnosed form of cancer -- other than skin cancer -- among American men, and is second only to lung cancer as a cause of cancer-related death among males. According to the American Cancer Society, almost 200,000 new cases of prostate cancer will be diagnosed this year, and about 30,000 patients will die of the disease.

The genistein used in the studies is a commercially made product manufactured by a Japanese company called Amino, which is co-sponsoring the studies with the UC Davis Department of Nutrition, White says.

White is now testing the effects of genistein on men with prostate cancer to see whether ingesting the soy extract lowers the levels of prostate specific antigen (PSA) in the blood. PSA is an enzyme measured in the blood that can rise if prostate abnormalities are present, according to the Centers for Disease Control and Prevention.

"We're doing a clinical study of 70 men with elevated PSA levels [to test the effect of genistein]," White says.

The men will be given genistein daily in pill form -- the amount will vary according to their body weights -- and their PSA levels will be tested at two, four and six months, White says. The results will be known in a year.

Tammy Hanna, nutritional research coordinator at the University of Kentucky in Lexington, says, "There really have been no clinical trials on humans [for genistein]. Because of its anti-carcinogenic quality, it could potentially be promising in humans."

In recent years, there has been much interest and research into whether eating soy products reduces the risk of breast cancer. Hanna says the studies of soy's effects on prostate cancer are in the same vein.

"The effect of the isoflavones could be promising in treating hormone-driven cancers," she says.

What To Do

If you'd like more information about clinical trials on prostate cancer, take a look at Veritas Medicine.

For more information about prostate cancer and its treatment, go to The American Cancer Society site. Interviews with researchers who have studied the effects of soy on health can be found at Soy.com.

HealthDay also has numerous articles on soy.

SOURCES: Interviews with Ralph deVere White, M.D., director, University of California at Davis Cancer Center; Tammy Hanna, nutritional research coordinator, University of Kentucky, Lexington; annual meeting, American Urological Association, Anaheim, Calif.
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