Pretreatment CT-derived body composition adds prognostic value beyond clinical-inflammatory factors in esophageal squamous cell carcinoma: a two-center retrospective development and external validation study

CT-derived body composition is associated with outcomes in esophageal cancer, but its added value beyond routine pretreatment risk assessment remains uncertain. We evaluated whether pretreatment L3 body composition improves survival prediction beyond a prespecified clinical-inflammatory model in ESCC treated with definitive concurrent chemoradiotherapy. This retrospective two-center study included 296 patients with nonmetastatic ESCC (development, n = 201; external validation, n = 95). Skeletal muscle index (SMI), skeletal muscle radiation attenuation (SMRA), visceral-to-subcutaneous adipose tissue ratio (VAT/SAT), and intermuscular adipose tissue index (IMATI) were measured on portal venous phase CT at L3. A clinical-inflammatory reference model (Model A) was compared with Model B, which added the four CT measures. Cox models underwent 1000-resample bootstrap internal validation and locked external validation without refitting or recalibration. In development, Model B increased the optimism-corrected C-index from 0.606 to 0.659 (difference, 0.053; 95% CI, 0.020–0.091) and 3-year AUC from 0.672 to 0.751. In external validation, the C-index increased from 0.657 to 0.721 (difference, 0.063; 95% CI, 0.017–0.116) and 3-year AUC from 0.690 to 0.772 (difference, 0.082; 95% CI, 0.015–0.192). The 3-year Brier score improved from 0.221 to 0.185. External calibration slope was 1.17, with modest mortality overprediction (55.7% predicted vs. 49.2% observed). SMRA showed the strongest individual imaging association with mortality. Pretreatment CT-derived body composition improved survival prediction beyond clinical-inflammatory factors in ESCC, and the improvement was maintained in regional external validation. Broader multicenter validation is required before clinical implementation.