Antiestrogen therapy of breast cancer

Studies in vitro and in animal models have helped define the mechanism of action of antiestrogens and the differences in the physical properties of the various antiestrogens. Tamoxifen is the most widely studied antiestrogen. A review of 45 separate studies has shown a response rate to tamoxifen in advanced breast cancer that varies between 14% and 57%, with an overall response rate of 34%; prior therapy strongly influenced response rate. Menopausal status did not seem to influence response, and no dose-response relationship has been documented. Patients with estrogen-receptor-positive tumors are more likely to respond than those with estrogen-receptor-negative disease. Tamoxifen has been shown to be an unusually safe and well-tolerated drug. Studies of antiestrogens as adjuvants to local therapy of early breast cancer have generally produced encouraging results. More studies are needed, however, in order to define those subsets of patients who are most likely to benefit from adjuvant therapy with tamoxifen and to determine the most effective regimens.