Exemestane in breast cancer: current status and future directions

Exemestane is a novel, potent, and specific third-generation aromatase inactivator developed for breast can-cer therapy. The drug is effective in patients with metastatic disease failing tamoxifen alone or tamoxifen followed by megestrol acetate or a nonsteroidal aromatase inhibitor. In a phase III study, exemestane was superior to megestrol acetate in overall survival, time to tumor progression, and time to treatment failure in women with metastatic disease who experienced failure of tamoxifen. Preliminary evidence suggests activity to exemestane exceeds that obtained with tamoxifen as first-line treatment. Two studies are comparing sequential treatment with tamoxifen followed by exemestane to tamoxifen monotherapy in the adjuvant setting. A third study is comparing the toxicity profile of exemestane with that of placebo in patients with early breast cancer who are at low risk of relapse. The findings from these studies will determine the role of exemestane in early breast cancer and lay the foundation for assessing its potential role in breast cancer prevention.