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Drugs Prevent Breast Cancer -- for Some

Few Now Benefit; Safer Drugs Needed
By
WebMD Health News
Reviewed by Gary D. Vogin, MD

July 1, 2002 -- There's no doubt that new drugs called SERMs can prevent breast cancer. The problem is that nobody's quite sure how to use them -- yet.

The drugs are tamoxifen (sold as Nolvadex) and Evista. They are drugs that act like estrogen on some cells in the body and in other cells block the action of estrogen. Clinical trials show that both drugs can prevent breast cancers that need estrogen to grow. So far, the FDA has approved only tamoxifen for breast cancer prevention. Evista is FDA approved for treating bone loss after menopause.

Eli Lilly and Company, the maker of Evista, is a WebMD sponsor.

A team of distinguished breast cancer experts took a look at all clinical trials of the two drugs. Their report -- upon which the U.S. Preventive Services Task Force will base its official recommendations -- appears in the July 2 issue of Annals of Internal Medicine. Lead author Linda Kinsinger, MD, MPH, is co-director of the prevention program at the University of North Carolina School of Medicine in Chapel Hill.

"The bottom line is that these medicines offer some promising opportunities," Kinsinger tells WebMD. "The target group is still small, no more than 10% of women in general. The drugs are not for everyone. But for one group -- women generally in their 40s to 50s with increased risk of breast cancer but who don't have increased risk for the drugs' side effects -- these women should talk with their doctors about them."

European studies failed to find a prevention benefit for tamoxifen. While Kinsinger and her fellow experts can't entirely explain this, they suggest that too few women in these studies took the drug long enough for maximum effect. Also, these studies may have had too few women with estrogen-sensitive breast cancer.

A large U.S. study got much different results. It looked at more than 13,000 women age 35 or older with a relatively high risk of breast cancer. It showed that tamoxifen cut breast cancer risk in half. To prevent one case of breast cancer, the study showed, 47 women would have to take tamoxifen for five years.

There's been only one large study of Evista's ability to prevent breast cancer. It looked at a different group of women: 7,705 postmenopausal women with osteoporosis. In this group, Evista cut breast cancer risk by 76%. To prevent one case of breast cancer, 126 women would have to take Evista for 40 months.

Both tamoxifen and Evista have side effects. Both increase the risk of blood clots in the legs and lungs, Kinsinger says. But she's quick to point out that this risk is no greater than the risk of taking estrogen-containing hormone-replacement therapy. Unlike Evista, tamoxifen increases a woman's risk of uterine cancer. Each drug also has other annoying but less drastic side effects.

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