Most women diagnosed with breast cancer have tumors that grow in the presence of estrogen. The anti-estrogen therapies that have been developed to treat these tumors cut the risk for cancer recurrence in half, and reduce deaths by about one-third. Tamoxifen, which has been used and researched for decades, works by binding to the estrogen receptor, which keeps estrogen from getting into the cancer cells to stimulate their growth.
The newer aromatase inhibitors (AI), which include letrrozole (Femara), anastrozole (Arimidex) and exemestane (Aromasin), appear to be even more effective in reducing recurrence and death. The AIs, as they are called, work in a different way than tamoxifen does. These drugs inhibit an enzyme called aromatase, which converts androgens (male hormones) to estrogen. Unlike tamoxifen, which can be used by both pre- and postmenopausal women, the AIs can only be used by postmenopausal women.
