A 61-year-old woman started on anastrozole for ER-positive early breast cancer presents two years later with severe mid-back pain. Radiographs show a compression fracture of T8, and DEXA reveals a T score of -3.0. What is the underlying mechanism?

• A Direct inhibition of osteoblast activity by the aromatase inhibitor
• B Osteomalacia secondary to drug induced vitamin D deficiency
• C Profound peripheral oestrogen deprivation accelerating bone resorption ✓
• D Glucocorticoid like mineralocorticoid effect of the drug on bone

Explanation

Non-steroidal aromatase inhibitors abolish conversion of adrenal androgens to oestrogen in peripheral fat, dropping circulating oestradiol far below natural postmenopausal levels. Since oestrogen suppresses osteoclast mediated resorption, its depletion accelerates bone loss and fracture risk, unlike tamoxifen which is bone protective after menopause. The drug does not inhibit osteoblasts directly or mimic glucocorticoids, excluding A and D, and patients need baseline DEXA monitoring with calcium, vitamin D and bisphosphonates when indicated.

Reference: Williams Textbook of Endocrinology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.