A 62-year-old postmenopausal woman with ER-positive early breast cancer is started on letrozole. By what mechanism does this drug act?

• A Competitive antagonism at the oestrogen receptor
• B Selective oestrogen receptor modulation in breast tissue
• C Suppression of pituitary FSH and LH secretion
• D Inhibition of peripheral conversion of adrenal androgens to oestradiol ✓

Explanation

Letrozole is a non-steroidal aromatase inhibitor blocking conversion of adrenal androstenedione and testosterone to oestrone and oestradiol in peripheral fat, muscle and breast tissue, the dominant oestrogen source after menopause. Tamoxifen is the competitive receptor antagonist, raloxifene is the SERM, and GnRH analogues suppress pituitary gonadotropins, which matters only in premenopausal women whose ovaries remain the main oestrogen source.

Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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