About letrozolenon-steroidal aromatase inhibitor, antineoplastic.mechanism of action of letrozolethis aromatase enzyme inhibitor, competitively and reversibly bind to the heme portion of cytochrome p450 unit of aromatase enzyme (which convert the androgens to estrogens) and inhibit its activity. it causes the reduction in plasma estrogen level and then the growth of estrogen related tumors growth. indications for letrozole1. breast cancer especially in post menopausal woman. 2. pre-operative treatment in post-menopausal women with localized hormone-receptor-positive breast cancer. typical dosage for letrozoleoral- adult- 2.5mg once daily. contra-indications of letrozole1. hypersensitivity to the drug and its components 2. severe hepatic impairment 3. premenopausal woman