About Letrozole Non-steroidal Aromatase Inhibitor, Antineoplastic. Mechanism of Action of Letrozole This 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 Letrozole 1. 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 Letrozole Oral- Adult- 2.5mg once daily. Contra-indications of Letrozole 1. Hypersensitivity to the drug and its components 2. Severe hepatic impairment 3. Premenopausal woman