Letrozole (Femara®) is an oral non-steroidal aromatase inhibitor that has been introduced for the adjuvant treatment of hormonally-responsive breast cancer. more...
Estrogens are produced by the conversion of androgens through the activity of the aromatase enzyme. Letrozole blocks this activity 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, Tamoxifen, the major medical therapy prior to the arrival of aromatase inhibitors, does effect its antiestrogenic action by interfering with the estrogen receptor, not the estrogen production.
Letrozole is approved by the FDA for the treatment of local or metastatic breast cancer that is hormone receptor positive or has an unknown receptor status. Side effects include signs and symptoms of hypoestrogenism. There is concern that long term use may lead to osteoporosis.
A related agent is anastrozole.
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