Weighing the risks and benefits of tamoxifen treatment for preventing breast cancer

Background: In response to findings from the Breast Cancer Prevention Trial that tamoxifen treatment produced a 49% reduction in the risk of invasive breast cancer in a population of women at elevated risk, the National Cance r Institute sponsored a workshop on July 7 and 8, 1998, to develop informat ion to assist in counseling and in weighing the risks and benefits of tamox ifen, Our study was undertaken to develop tools to identify women for whom the benefits outweigh the risks, Methods: Information was reviewed on the i ncidence of invasive breast cancer and of in situ lesions, as well as on se veral other health outcomes, in the absence of tamoxifen treatment. Data on the effects of tamoxifen on these outcomes were also reviewed, and methods were developed to compare the risks and benefits of tamoxifen, Results: Th e risks and benefits of tamoxifen depend on age and race, as well as on a w oman's specific risk factors for breast cancer, In particular, the absolute risks from tamoxifen of endometrial cancer, stroke, pulmonary embolism, an d deep vein thrombosis increase with age, and these absolute risks differ b etween white and black women, as does the protective effect of tamoxifen on fractures. Tables and aids are developed to describe the risks and benefit s of tamoxifen and to identify classes of women for whom the benefits outwe igh the risks. Conclusions: Tamoxifen is most beneficial for younger women with an elevated risk of breast cancer. The quantitative analyses presented can assist health care providers and women in weighing the risks and benef its of tamoxifen for reducing breast cancer risk.