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The manufacturer of the breast cancer drug, Femara (generic name letrozole), issued a warning that women who may be pregnant should avoid the drug because of an increased risk of birth defects. Femara is approved by the U.S. Food and Drug Administration (FDA) to treat women with advanced breast cancer. While U.S. labels on Femara warn of its possible dangers, there have been reports that some doctors prescribe Femara to women with fertility problems. Pregnant women who have taken Femara should contact their doctors. Femara belongs to a class of drugs called aromatase inhibitors and works differently than tamoxifen. To grow and reproduce, breast cancer cells require the female hormone estrogen. Femara works by reducing the total amount of estrogen in the body (circulating estrogen levels), thereby limiting the amount of estrogen that can affect breast cancer cells. Other examples of aromatase inhibitors include Arimidex (generic name, anastrozole) and Aromasin (generic name, exemestane). Both of these drugs are also used to help treat advanced breast cancer in women whose breast cancer tumors have not responded well to standard drug treatment with tamoxifen (brand name, Nolvadex). In 2004, a landmark study found that Femara significantly improves the chances of breast cancer survival when taken after five years of treatment with tamoxifen. The research-which was halted early to allow women in the study who were taking a placebo, or inactive pill, to reap the benefits of Femara-found that taking Femara after tamoxifen reduced the risk of a recurrence and death from breast cancer by nearly one half. The U.S. National Cancer Institute encourages breast cancer patients to discuss the possibility of taking Femara after five years of treatment with tamoxifen. In addition to treating breast cancer, it has been found that some doctors prescribe Femara to women who are having difficulty conceiving-even though U.S. labels of the drug warn that Femara should not be taken by women who are pregnant because of the risk of birth defects. Some research suggests that Femara may suppress estrogen and can stimulate ovulation. According to a study by Marinko Biljan, MD, director of the Montreal Fertility Center in Canada, and colleagues, Femara is increasingly used as a fertility drug because it appears to be safe. His research found that Femara is prescribed "off-the-label" in the United States and Canada, even though the drug is not approved by either country's government for use as an infertility treatment. However, his research also showed that birth defects occurred in children of 7 of 150 women taking Femara. Novartis Pharmaceuticals Canada Inc. and Health Canada recently warned Canadian doctors not to prescribe Femara to women for the purposes of becoming pregnant. According to the Novartis Canada statement, "the use of [Femara] for the purpose of ovulation induction is not within the scope of the approved indications." Novartis also sent a letter to U.S. fertility clinics warning them not to prescribe Femara. The U.S. FDA is currently considering whether to issue a warning about Femara.
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