External Validation of Biomechanical Computed Tomography for Fracture Risk Classification in Metastatic Hormone Sensitive Prostate Cancer.

e24077 Background: For men with metastatic hormone-sensitive prostate cancer (mHSPC) on androgen deprivation therapy (ADT), guidelines recommend dual-energy X-ray absorptiometry (DXA) screening to identify fracture risk and benefit from antiresorptive therapy. However, only 8% of men with mHSPC receive routine DXA screening. Biomechanical computed tomography (BCT) is a radiomic technique that measures bone mineral density (BMD) and bone strength from routine staging and surveillance CT scans but has not been validated in mHSPC. Methods: This retrospective cohort study included 99 patients with incident mHSPC beginning ADT (2013-2020) at one academic (n = 70) and one tertiary VA medical center (n = 29) with CT abdomen/pelvis or PET/CT imaging at baseline (within 1 year prior to ADT initiation) and follow-up (1-2 years after ADT initiation). BCT-assessed BMD T-score and femoral strength were calculated from baseline and follow-up CT scans. We evaluated the association between BCT measures and subsequent pathologic and non-pathologic fractures within 3 years following mHSPC diagnosis. Results: Among 99 patients, mean age was 68 years, 48 (48.5%) were White, and 45 (45.4%) were Black. During median follow-up of 19 months, 23 (24%) developed a pathologic and 15 (15%) a non-pathologic fracture. BCT and DXA-assessed femoral-neck BMD T-score were strongly correlated (R 2 = 0.94, N = 23). Higher BCT-assessed baseline BMD (Odds Ratio [OR] 0.5, p = 0.03) and bone strength (OR 0.57, p = 0.02) were each associated with decreased pathologic fracture (Table). Neither BMD nor bone strength were significantly associated with non-pathologic fracture. BCT identified 10 (10%) men eligible for antiresorptive therapy by established BMD, strength, or FRAX criteria at ADT initiation, 4 (40%) of whom never received it by the end of follow-up. Between baseline and follow-up, both BMD (-0.27) and bone strength (-0.34) decreased among patients who did not receive antiresorptive therapy (n = 76), with no difference in longitudinal change between ADT alone vs with androgen receptor signaling inhibitors. Conclusions: In this diverse, multicenter cohort of men with mHSPC beginning ADT, BCT BMD assessed from routine CT scans strongly correlated with DXA-assessed BMD. BCT measurements predicted subsequent pathologic fracture and identified additional men who would benefit from antiresorptive therapy. BCT may provide a practical method to assess the role for anti-resorptive therapy in patients with mHSPC. [Table: see text]