Letrozole: An oral antiestrogen. Letrozole inhibits the enzyme aromatase in the adrenal glands that produces the estrogens (estradiol and estrone) and thereby lowers their levels. It works by decreasing the amount of estrogen the body makes. This can slow or stop the growth of many types of breast cancer cells that need estrogen to grow. The brand name of letrozole is Femara.
See also: Aromatase inhibitor; monograph on Femara (letrozole).