Chemoprevention of breast cancer in postmenopausal women

In the United States, an estimated 211,240 new cases of breast cancer were diagnosed in 2005 and approximately 40,410 deaths occurred. In recent years, a number of randomized prospective trials have investigated the use of antiestrogens as a means to reduce the incidence of breast cancer. We aim to describe the results of these trials as they pertain to postmenopausal women. In the Breast Cancer Prevention Trial and the International Breast Cancer Intervention Study-I, tamoxifen reduced the risk of invasive breast cancer by 55% and 30%, respectively, among older participants. However, tamoxifen is associated with adverse events including thromboembolic disease and endometrial cancer. The Multiple Outcomes of Raloxifene Evaluation, aimed primarily at evaluating the use of raloxifene for the prevention of osteoporosis, demonstrated a 72% decreased breast cancer risk. Side effects of raloxifene include thromboembolic events, but not endometrial cancer. Results from the Study of Tamoxifen and Raloxifene trial comparing these two agents are expected in mid-2006. Ongoing chemoprevention trials are evaluating the use of the aromatase inhibitors. At present, tamoxifen is the only FDA-approved agent for breast cancer risk reduction. Decisions regarding its use must remain highly individualized, involving careful consideration of its risks versus benefits.