A 52-year-old postmenopausal woman who completed 5 years of adjuvant tamoxifen for ER-positive breast cancer presents with postmenopausal bleeding. Endometrial biopsy shows adenocarcinoma. The oncologic property of tamoxifen responsible is its action as:

• A An aromatase inhibitor increasing endometrial estrogen exposure
• B A pure estrogen receptor agonist in all tissues
• C An estrogen receptor antagonist in breast tissue and partial agonist in endometrium ✓
• D A selective estrogen receptor degrader with pure antagonism everywhere

Explanation

Tamoxifen is the prototype selective estrogen receptor modulator: it antagonizes estrogen receptors in breast but has partial agonist activity in endometrium, bone and liver. Chronic use therefore reduces breast cancer recurrence yet doubles to triples the risk of endometrial carcinoma, presenting as abnormal bleeding. Aromatase inhibitors lower estrogen everywhere and carry no meaningful endometrial cancer signal, and fulvestrant, the degrader, lacks agonist activity.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.