Anastrozole is a selective nonsteroidal aromatase inhibitor. Many breast cancers have estrogen receptors; the growth of these tumors is stimulated by estrogen. In postmenopausal women, the main source of estrogen is the conversion of adrenal androgen to estrogen (primarily estradiol) by aro-matase in the peripheral tissues, such as the adipose tissue.

Treatment of advanced breast cancer in postmenopausal women whose disease has progressed after tamoxifen therapy.