Breast cancer chemoprevention

A significant amount of evidence has accumulated from randomized clinical trials supporting the use of pharmacologic agents for breast cancer risk reduction. All of these trials have capitalized on the known expression of estrogen receptors on many breast cancer cells, and the demonstrated efficacy of selective estrogen receptor modulators (SERMs) to treat breast cancer. Two SERMs, tamoxifen and raloxifene, have been studied extensively in randomized, controlled trials, and both have been shown to reduce the risk of invasive ER-positive breast cancer by approximately 50% in women at increased risk. Other benefits that have been documented are a decrease in fractures for both drugs, and a decrease in noninvasive breast cancer and benign breast disease for tamoxifen. The risk of venous thromboembolic events and vasomotor symptoms is increased for both drugs. In addition, tamoxifen is associated with a twofold increase in endometrial cancer, and a modest increase in cataracts and cataract surgery. Studies are underway to explore the role of aromatase inhibitors for breast cancer risk reduction. In addition, several novel pharmacologic and natural compounds are being considered for future trials.