CHAMPAIGN, Ill. -- May 1, 2002 -- Supplementing one’s diet with soy and other nutritional aids rich in isovlavones and the derivative genistein may be the wrong thing to do for women battling estrogen-dependent breast cancer say researchers.
Postmenopausal women with estrogen-dependent breast cancer often face an emotional roller coaster. Physicians prescribe tamoxifen to suppress the tumors and recommend against the use of hormone-replacement therapy (HRT). While tamoxifen stops estrogen from stimulating breast cancer cells, it also can cause menopausal symptoms. Some women turn to over-the-counter products containing isoflavones as an alternative to HRT to treat their menopausal symptoms.
In a study in mice, a research team led by Dr. William Helferich at the University of Illinois at Urbana-Champaign. found that isoflavone-enhanced dietary supplements containing genistein counteracted the tumor-fighting effects of tamoxifen, a commonly prescribed medication for women whose breast tumors have estrogen receptors. The findings appear in the May 1 issue of the journal Cancer Research.
“This new study takes our previous findings a step further,” Helferich said in a press release. “These results raise concern about consuming dietary isoflavone supplements in conjunction with tamoxifen in postmenopausal women who have estrogen-dependent breast cancer.”
In a series of studies published last year, Helferich’s laboratory demonstrated that various dietary products containing genistein can stimulate the growth of estrogen-dependent human breast tumors implanted into adult mice.
In this current study, researchers divided 66 mice, with their ovaries removed, into six groups to monitor the effects of estrogen and various amounts of tamoxifen and genistein, an estrogen-like component found in legume plants such as soy, peas and certain beans.
Before adding genistein to the diet, the tamoxifen had stopped tumor growth. The addition of genistein resulted in enhanced growth of estrogen-dependent tumors and increases in estrogen-responsive gene markers.
Blood concentrations of genistein in these mice were similar to those levels that people can get by consuming isoflavone-rich dietary supplements, Helferich said.
Genistein often is identified as one of several desired isoflavones in soy products, including soy-enhanced drinks and dietary supplements.
Ironically, isoflavones in soy are believed to be responsible for anti-cancer effects observed in numerous human and animal studies. In Asia, where cancer rates are low, people often consume diets rich in soy products that contain about 20 to 30 milligrams of isoflavones a day, Helferich said. However, many isoflavone-enhanced drinks and supplements now available in the United States may contain 30 to 150 milligrams per serving, and two or more servings a day are recommended on the labels, he added.
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