A 45-year-old woman with estrogen receptor-positive breast cancer is started on adjuvant tamoxifen. The mechanism by which tamoxifen exerts its anti-neoplastic effect in breast tissue is:
- A Competitive antagonism of estrogen receptors in breast tissue ✓
- B Aromatase inhibition reducing estrogen synthesis
- C Downregulation of estrogen receptor expression
- D Progesterone receptor agonism opposing estrogen effects
Correct answer: A. Competitive antagonism of estrogen receptors in breast tissue
Explanation
Tamoxifen is a selective estrogen receptor modulator (SERM) that acts as a competitive antagonist of estrogen receptors in breast tissue, thereby blocking estrogen-mediated proliferation of ER-positive breast cancer cells. It is an antagonist in breast but a partial agonist in endometrium and bone. Aromatase inhibitors like letrozole work by a different mechanism (option B), and the two are not interchangeable in all settings.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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