Nonsteroidal and steroidal aromatase inhibitors in breast cancer

Anastrozole (Arimidex), letrozole (Femara), and exemestane (Aromasin) are members of the third generation of aromatase inhibitors that has now replaced aminoglutethimide (Cytadren), the progestins, and tamoxifen (Nolvadex) as the hormonal therapy of choice in estrogen-receptor-positive, postmenopausal, metastatic breast cancer. This article will review the role of aromatase in the pathogenesis of breast cancer and the results of recent studies that have established the role of its inhibitors in estrogen-receptor-positive breast cancer. We will also briefly outline the rationale and design of ongoing studies.