Association between skeletal muscle morphometrics and overall survival among older adults with gastrointestinal cancers.

808 Background: Older adults with gastrointestinal (GI) cancers face a higher risk of treatment toxicities and adverse survival outcomes. However, the variability in these outcomes remains poorly understood. Age-related changes, including the progressive loss of skeletal muscle and gain in adipose tissue, contribute to this heterogeneity. Recent studies highlight an association between skeletal muscle gauge (SMG) and overall survival (OS) in older cancer patients, but its relevance among those with GI cancers is unclear. Methods: We included adults aged ≥ 60 years with newly diagnosed GI cancers, enrolled in the University of Alabama at Birmingham (UAB) Cancer and Aging Resilience Evaluation (CARE) registry between October 2017 and April 2024. Skeletal muscle index (SMI; skeletal muscle area in m²/height in cm) and skeletal muscle radiodensity (SMD; Hounsfield units) were derived from single-slice computed tomography (CT) staging scans at the third lumbar vertebra (L3) using validated methods. SMG was calculated as the product of SMI and SMD, reported in arbitrary units (AU). Participants were followed until death or the study cutoff date of July 10, 2024. Kaplan-Meier survival analysis was used to estimate OS by SMG status (low: < median; high: ≥ median). Cox proportional hazards models were employed to assess the relationship between SMG and OS, adjusting for age, sex, race/ethnicity, and cancer stage. Results: A total of 568 patients were included in the study, with a median age at diagnosis of 68 years (interquartile range, IQR: 64-74), 55% male, 73% non-Hispanic White, and 43% were diagnosed with Stage IV disease. Colorectal (33%) and pancreatic (27%) cancers were the most common diagnoses. The median SMG was 1,529 AU (IQR: 1,151–1,967). Over a median follow-up of 60 months, 367 patients (64%) died. Median OS was 19 months for those with low SMG and 26 months for those with high SMG (log-rank test, p < .05). After adjustment for confounders, SMG remained independently associated with OS (adjusted Hazard Ratio: 0.678 per IQR increase; 95% CI: 0.57– 0.807; p < .001), indicating that each IQR increase in SMG is associated with a decrease in all-cause mortality risk by 32.2%. Conclusions: Skeletal muscle gauge, an integrated measure of SMI and SMD, is significantly associated with improved survival among older adults with GI cancers. Further research is needed to determine whether SMG has a causal impact on survival in this population.