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Estrogen and Breast Cancer

New studies finds that drugs that block estrogen may reduce the risk of breast cancer for 10 years in women. Postmenopausal women in the studies who took drugs called selective estrogen receptor modulators (SERMs), such as tamoxifen, were 38 percent less likely to develop any type of breast cancer over a 10-year period, compared with women who weren’t taking SERMs. The studies also involved the SERMs raloxifene, arzoxifene and lasofoxifene.

Only tamoxifen and raloxifene are approved by the Food and Drug Administration for the prevention of breast cancer, and only tamoxifen is approved for use in premenopausal women who are at high risk for breast cancer. The other drugs in the studies are currently being studied as treatments for osteoporosis, but they also lower the risk of breast cancer, Jordan said.

The drugs come with side effects that have made women reluctant to take them, he said. The common side effects are similar to symptoms of menopause, including hot flashes and vaginal dryness.

In the new review, researchers looked at nine studies involving more than 83,000 women. Eight of the studies compared taking a SERM with taking a placebo, while one study compared raloxifene to tamoxifen.

Researchers found that 4.2 percent of women taking a SERM developed breast cancer, while 6.3 percent of women in the control groups developed breast cancer.

The reduction in risk was primarily seen with estrogen-receptor positive breast cancers, which are fueled by estrogen, according to the study.

The study is published online Tuesday (April 30) in the journal Lancet.

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