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letrozole, anticancer drug used to inhibit the synthesis of estrogen in postmenopausal women who have breast cancers that are dependent on the growth-promoting actions of the hormone. Letrozole is marketed as Femara and is manufactured by Swiss drug company Novartis AG. Letrozole is taken orally and works by inhibiting the conversion of testosterone to estrogen. The drug specifically targets an enzyme called aromatase, which catalyzes the formation of estrogens from androgens, such as testosterone. For...