Letrozole (
INN, trade name Femara®) is an oral non-steroidal
aromatase inhibitor that has been introduced for the adjuvant treatment of hormonally-responsive
breast cancerEstrogens are produced by the conversion of
androgens through the activity of the
aromatase enzyme. Letrozole blocks production of estrogens in this way by competitive, reversible binding to the heme of its
cytochrome P450 unit. The action is specific, and letrozole does not reduce production of mineralo- or corticosteroids. In contrast, the antiestrogenic action of
tamoxifen, the major medical therapy prior to the arrival of aromatase inhibitors, is due to its interfering with the estrogen receptor, rather than inhibiting estrogen production.
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