A 56-year-old postmenopausal woman on adjuvant tamoxifen for ER-positive breast cancer presents with postmenopausal vaginal bleeding. Endometrial sampling shows adenocarcinoma. The most likely explanation is:
- A Tamoxifen acts as a pure estrogen antagonist on endometrial tissue
- B Metastatic spread of breast carcinoma to the uterus
- C Tamoxifen has partial estrogen agonist activity on the endometrium ✓
- D Unmasking of a pre-existing ovarian granulosa cell tumor
Correct answer: C. Tamoxifen has partial estrogen agonist activity on the endometrium
Explanation
Tamoxifen is a selective estrogen receptor modulator: it antagonizes estrogen in breast tissue but behaves as a partial agonist in the endometrium and bone. Chronic stimulation of the endometrium raises the risk of endometrial hyperplasia and carcinoma, and abnormal bleeding in a tamoxifen-treated patient mandates evaluation. Metastatic breast cancer to the endometrium is distinctly uncommon compared with this well documented drug effect described in Harrison and Williams.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.