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AI-induced Osteoporosis — SCE Medical Oncology MCQ

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EasyBreast CancerAI-induced OsteoporosisSCE Medical Oncology

A 60-year-old woman with ER+/HER2- breast cancer has been on letrozole for 4 years. She develops a new vertebral compression fracture. DEXA scan shows T-score -2.9 (osteoporosis). What is the mechanism of AI-induced bone loss?

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Correct answer: B — Aromatase inhibitors eliminate residual peripheral oestrogen synthesis in postmenopausal women, removing oestrogen's bone-protective effects — accelerated bone loss occurs at approximately 2× the natural postmenopausal rate

AIs block the aromatase enzyme (CYP19A1) converting androgens to oestrogens in peripheral tissues. This eliminates residual postmenopausal oestrogen production, removing oestrogen's inhibitory effect on osteoclast activity. The result is accelerated bone resorption (2-3% annual bone density loss vs 1% natural menopause). Management includes: baseline and serial DEXA, calcium + vitamin D supplementation, weight-bearing exercise, and bisphosphonates/denosumab for osteoporosis or high fracture risk (FRAX assessment).

Reference: BNF Letrozole; NICE NG101; ESMO 2024 Bone Health; ATAC bone sub-study