Dear river1980, Both Femara (letrozole) and Arimidex (anastrozole) are aromatase inhibitors used in the treatment of hormone
receptor positive breast cancer in post menopausal women. Aromatase inhibitors block the enzyme aromatase (found in the body's muscle, skin, breast and fat), which is used to convert androgens (hormones produced by the adrenal glands) into estrogen. In the absence of estrogen, tumors dependent on this hormone for growth will shrink.