Body Composition as an Independent Predictive and Prognostic Biomarker in Advanced Urothelial Carcinoma Patients Treated with Immune Checkpoint Inhibitors

Background Several immune checkpoint inhibitors (ICIs) are approved for the treatment of advanced urothelial carcinoma (UC). There are limited biomarkers for ICI‐treated patients with UC. We investigated the association between body composition and clinical outcomes in ICI‐treated UC patients. Materials and Methods We conducted a retrospective analysis of 70 ICI‐treated patients with advanced UC at Winship Cancer Institute from 2015 to 2020. Baseline computed tomography images within 2 months of ICI initiation were collected at mid‐L3 and muscle and fat compartments (subcutaneous, intermuscular, and visceral) were segmented using SliceOMatic v5.0 (TomoVision, Magog, Canada). A prognostic body composition risk score (high: 0–1, intermediate: 2–3, or low‐risk: 4) was created based on the β coefficient from the multivariate Cox model (MVA) following best‐subset variable selection. Our body composition risk score was skeletal muscle index (SMI) + 2 × attenuated skeletal muscle (SM) mean + visceral fat index (VFI). Concordance statistics (C‐statistics) were used to quantify the discriminatory magnitude of the predictive model. Results Most patients (70%) were men and the majority received ICIs in the second‐ (46%) or third‐line (21%) setting. High‐risk patients had significantly shorter overall survival (OS; hazard ratio [HR], 6.72; p