Aromatase Inhibitors

Aromatase inhibitors aren't new. The FDA approved the first, Arimidex, in September 2000. Many large trials have recently confirmed that these hormone therapies outperform the more commonly used tamoxifen to prevent tumor recurrence in women who had hormone-positive breast cancers (cancers that are fed by estrogen).

Because they act only on estrogen that's produced outside the ovaries, aromatase inhibitors are only effective in postmenopausal women. (Before menopause, most of the body's estrogen is produced in the ovaries.) But for these women, Arimidex and its sister drugs, like Aromasin and Femara, offer a small but crucial advantage over tamoxifen -- 4% to 5% -- in preventing cancer recurrence. Researchers still don't know which strategy works best: taking an aromatase inhibitor instead of tamoxifen, as the first course of therapy after surgery for breast cancer (called adjuvant therapy) or beginning treatment with tamoxifen and switching to an aromatase inhibitor after two to five years.