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Millions Could Benefit From Tamoxifen

Benefits Outweigh Risks of Breast Cancer Drug for Many Women

WebMD Health News

April 1, 2003 - More than two million women at high risk for developing breast cancer in the U.S. may still benefit from taking the breast cancer prevention drug tamoxifen, despite the well-known risks associated with the drug. A new study suggests that use of the tamoxifen could prevent nearly half of the breast cancers otherwise expected to occur in these women.

Tamoxifen has been shown to reduce the risk of recurrent breast cancer in women diagnosed with advanced breast cancer and help prevent the development of breast cancer in the non-affected breast. But the drug has also been associated serious side effect such as an increased risk of endometrial cancer, pulmonary embolism, stroke and deep vein thrombosis.

The results of the Breast Cancer Prevention Trial released in 1998 found women at high risk for breast cancer who took tamoxifen for five years had a 49% lower risk of breast cancer.

Those results prompted the FDA to approve the use of tamoxifen among high-risk women 35 years old and older who have a five-year risk of invasive breast cancer of 1.67% or higher.

Based on national data on cancer risk factors, researchers at the National Cancer Institute (NCI) calculated the number of women in the U.S. who would be eligible for treatment according to the FDA's criteria. They then estimated the number of women for whom the benefits of tamoxifen would outweigh the risks.

Andrew N. Freedman, PhD, of the NCI, and colleagues estimated that 15.5% or 10,232,816 women would be eligible for tamoxifen treatment based on breast cancer risk alone. The percentage of women who would benefit from the treatment related to age and differed according race. Younger women are less likely to experience the adverse effects of the drug than older women, and the younger women would also most likely have a better overall benefit.

Researchers say differences in benefit also affected the level of risk the women faced. Among white women, they found the benefits outweighed the risks for about 5%, or 2.4 million. But only about 0.6% or 42,768 black women would benefit from tamoxifen because they face a higher risk for stroke, pulmonary embolism, and deep vein thrombosis.

Without treatment, researchers estimate that 58,148 invasive breast cancers would be expected to develop among the 2.4 million white women. If these women took tamoxifen over the next five years, the number of breast cancers would be reduced by 49% to 28,492.

Researchers say that although the risks far outweigh the benefits of tamoxifen for the majority of women eligible for treatment, their study shows that a sizable number of women would still greatly benefit from treatment despite the risks.

SOURCE: Journal of the National Cancer Institute, April 2, 2003.

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