Genistein-containing supplements may stop tamoxifen.(Brief Article)

2002 MAY 30 - (NewsRx.com & NewsRx.net) -- Isoflavone-enhanced dietary supplements containing genistein may negate the tumor-fighting effects of tamoxifen, a commonly prescribed medication for women battling estrogen-dependent breast cancer, according to new findings appearing in the May 1, 2002, issue of the journal Cancer Research.

The research was led by William G. Helferich, a professor of food science and human nutrition at the University of Illinois at Urbana-Champaign.

In a preclinical study, researchers divided 66 mice, with their ovaries removed, into 6 groups to monitor the effects of estrogen and various amounts of tamoxifen and genistein, an estrogen-like component found in legume plants. Estrogen and tamoxifen implants were put into the mice, and estrogen-dependent breast cancer cells were injected. 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.

"Previous studies in rodents have suggested that exposure to genistein early in life may prevent or delay breast cancer," Helferich said. However, 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.

"This new study takes our previous findings a step further," Helferich said. "These results raise concern about consuming dietary ...