Real-World Effectiveness of Denosumab and Bisphosphonates on Risk of Vertebral Fractures in Women with Breast Cancer Undergoing Treatment with Aromatase Inhibitors

Bone-active drugs are recommended to protect the skeleton from detrimental actions of aromatase inhibitors (AIs). However, most of literature data are focused on bone mineral density (BMD), whereas data on fractures are scant. The aim of this prospective study was to investigate the real-life effectiveness of denosumab, oral bisphosphonates (BPs) and intravenous zoledronate on risk of vertebral fractures (VFs) induced by AIs. 567 consecutive women (median age 62 years, range 28-83) with early breast cancer undergoing treatment with AIs were evaluated for morphometric VFs and BMD at baseline and after 18-24 months of follow-up. After enrollment, 268 women (47.3%) started denosumab 60 mg subcutaneously every 6 months, 115 (20.3%) BPs (59 with oral BPs and, 56 with intravenous zoledronate 5 mg/12 months), whereas 184 women (32.5%) were not treated with bone-active drugs for several reasons. During follow-up, 54 women (9.5%) developed incident VFs in association with age of subjects (P < 0.001), baseline FRAX scores for major fractures (P < 0.001) and hip fractures (P = 0.003), pre-existing VFs (P < 0.001), change in BMD at lumbar spine (P = 0.015), femoral neck (P = 0.003) and total hip (P < 0.001). Risk of VFs was higher in subjects who were untreated as compared to those treated with bone-active drugs (32/184 vs. 22/383; P < 0.001). Specifically, fracture risk was significantly decreased by denosumab [odds ratio (OR) 0.22; P < 0.001] and zoledronate (OR 0.27; P = 0.035), but not by oral BPs (P = 0.317). These data suggest that in real-world clinical practice, denosumab and zoledronate can reduce AI-related risk of VFs after only 24 months of treatment.