Estrogen manipulation represents an effective treatment for advanced breast cancer in postmenopausal women with estrogen-receptor-positive disease. The antiestrogen agent, tamoxifen, is the first choice for advanced breast cancer in postmenopausal women due to its efficacy and lack of significant side effects. As with all cancer treatments, however, cancer may recur after initial treatment with tamoxifen, and the limitations of currently available alternative hormonal therapies in terms of tolerability and convenience of administration underscore the need for new agents. Anastrozole is a new, highly selective, nonsteroidal aromatase inhibitor capable of maximal estrogen depletion with fewer side effects than other hormonal therapies. Anastrozole is administered in a convenient, once-daily oral dosing regimen and does not require steroid replacement therapy. In two multicenter clinical trials, anastrozole was as effective as megestrol acetate for the treatment of advanced breast cancer in postmenopausal women who progressed after tamoxifen therapy, based on objective response rates and time to objective progression of disease. In addition, the drug did not produce the weight gain observed with megestrol acetate therapy. Anastrozole is an effective endocrine agent in the treatment of advanced breast cancer in postmenopausal women.