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Breast Cancer Health Center

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National Cancer Institute Summarizes Risks, Benefits of Tamoxifen

WebMD Health News

Nov. 12, 1999 (Atlanta) -- In response to research findings about the effectiveness of tamoxifen in preventing breast cancer, the National Cancer Institute (NCI) has developed an assessment tool to help patients and physicians weigh the relative risks and rewards of taking the drug. The NCI says the tool is designed to allow women to decide if chemoprevention with tamoxifen is right for them.

Tamoxifen is a medication used in the treatment of breast cancer and has also been effective in preventing breast cancer in some patients. It interferes with the activity of the female hormone estrogen. Estrogen stimulates the growth of breast cancer cells. Because of its anti-estrogen effects, tamoxifen, marketed as Nolvadex, has been found to lower blood cholesterol and reduce bone loss in osteoporosis. However, the drug has also been associated with adverse side effects such as increased endometrial cancer, stroke, and blood clots.

In a 6-year study of women at high risk for breast cancer, tamoxifen was shown to reduce the risk of invasive and noninvasive breast cancer by almost half. Additionally, there was a reduction in the incidence of fractures. Some women also developed life-threatening side effects including endometrial cancer, stroke, and blood clots. Because age and race are known to be risk factors for these adverse effects, NCI recommends that physicians base tamoxifen treatment decisions on profiles of patient risk.

Recently, a panel of experts reviewed the incidence of breast cancer, endometrial cancer, stroke, and blood clots with and without tamoxifen treatment. Using this data, the panel developed 13 summary tables for informed decision-making.

First, the 5-year risk of invasive breast cancer is estimated by using the following data: age at first menstrual period, age at first childbirth, family history of breast cancer, and number of benign and abnormal breast biopsies. Next, the overall benefit of tamoxifen treatment is determined with consideration to age and race. Finally, the magnitude of the benefit is evaluated. Tamoxifen was found to benefit young women the most.

Michael Gail, MD, PhD, the chief author of the NCI report, tells WebMD, "In women over 50, tamoxifen reduced fractures substantially, although it increased the risk of stroke and blood clots in African Americans and endometrial cancer in Caucasians." By comparison, tamoxifen caused very few adverse events in women under 50, black or white. Regardless of age and race, doctors say tamoxifen treatment requires close medical supervision.

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