277P Fat body mass independently predicts incident vertebral fractures in breast cancer patients given adjuvant aromatase inhibitor therapy and denosumab

Women with early breast cancer (EBC) receiving adjuvant aromatase inhibitors (AIs) are frequently given denosumab (Den) with the aim to both reducing fracture risk and preventing disease recurrence. However, a proportion of these patients still experience fragility fractures despite Den, and risk factors in women treated with upfront AIs and Den have never been explored. Dual-X-ray absorptiometry (DXA) at baseline conditions and after 18 months was performed in 237 consecutive patients undergoing adjuvant therapy with AIs and Den (60 mg subcutaneously every 6 months), recruited at the Breast Unit of the ASST-Spedali Civili of Brescia. The following baseline parameters were evaluated to predict the risk of vertebral fracture (VF) as assessed by a morphometric approach on DXA images: age, body mass index (BMI), history of previous fractures, family history of fractures, smoking, alcohol consumption, FRAX score, DXA-derived bone mineral density (BMD), trabecular bone score (TBS), percentage fat body mass (%FBM), lean body mass (LBM), appendicular mass index (ALMI). Seventeen out of 237 (7%) reported incident VFs after 18 months of AIs therapy. At the univariate analysis, incident VFs were significantly associated with high FRAX score (Odd Ratio [OR]: 3.786, 95% Confidence interval [CI]: 1.039-13.790), previous VFs (OR: 3.217, 95% CI: 1.185-8.736), high %FBM (OR 5.174, 95% CI: 1.418-18.873, p=0.013), high android fat (OR 9.580, 95% CI: 1.174-78.209, p=0.035) and low ALMI/FBM ratio (OR 0.252, 95% CI: 0.078-0.818, p=0.022). Only high %FBM was independently associated to incident VFs at multivariate analysis. FBM is an independent risk factor for VFs in EBC patients treated with adjuvant AIs and Den. A supervised physical activity aiming at avoiding obesity and potentiating LBM could synergize with Den in preventing AI-induced bone fragility.