Supplementary Material for: Prognostic effect of impaired skeletal muscle assessed with computed tomography images in patients with endoscopic resection for esophageal squamous cell carcinoma

Introduction: No studies have investigated the prognostic effect of skeletal muscle mass and quality and adipose tissue distribution in patients who undergo endoscopic resection (ER) for esophageal squamous cell carcinoma (ESCC). Thus, this study aimed to evaluate their association. Methods: We retrospectively collected data from patients who underwent ER for ESCC at our institution between 2005 and 2020. Multivariate Cox analysis was performed to investigate the association of 17 candidate factors, including indices for skeletal muscle mass and quality and adipose tissue distribution assessed with computed tomography (CT) images, with prognosis. Further, we evaluated the association of impaired skeletal muscle, characterized by the combination of low skeletal mass index (SMI) and high intramuscular adipose tissue content (IMAC), with prognosis and early and late mortality. Results: Among 450 patients, 116 (25.8%) died during the median follow-up of 111.6 months. Multivariate analyses revealed low SMI (hazard ratio [HR], 1.65) and high visceral adipose index (HR, 0.48) showed significant association with mortality, in addition to male sex, performance status, Charlson comorbidity index, American Society of Anesthesiologists physical status, and prognostic nutrition index. Conversely, no significant association was revealed in other indices. Impaired skeletal muscle was a risk factor for mortality (HR, 2.87) but not the combination of low SMI and low IMAC. It was significantly associated with late mortality (HR, 4.53) but not with early mortality. Conclusion: Impaired skeletal muscle assessed with CT images was a risk factor for late mortality in patients who underwent ER for ESCC.