An herbal extract that some women use to relieve symptoms of menopause increases the likelihood in mice with breast cancer that the disease will spread, researchers have found.

The extract, called black cohosh, is especially popular among women who have developed breast cancer, because hormone-replacement therapy for menopausal symptoms isn't recommended for such women.

Some studies have suggested that black cohosh acts as a sex hormone, a trait that could affect breast cancers in women who take it. To investigate that possibility, Vicki L. Davis of Duquesne University in Pittsburgh and her colleagues fed black cohosh to mice that were genetically predisposed to develop breast cancer. The researchers gave other mice of that breed a diet free of hormone-mimicking plant compounds.

Black cohosh didn't affect the animals' likelihood of developing breast cancer or how quickly tumors arose, but after 14 months, animals that had received the extract were 2.5 times as likely as the other mice were to have visible tumors in their lungs, Davis reports.

In other experiments, Sara Rockwell of Yale University found that breast cancer cells exposed to either of two antitumor drugs were more likely to die if they were also exposed to black cohosh extract. That could make the extract useful in fighting breast cancer. However, Rockwell says, if black cohosh also intensifies the drug's cell-killing powers in the bone marrow and heart, it could substantially increase toxic side effects in those parts of the body. --B.H.

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