Low muscle mass, obesity, and cause-specific mortality in cancer patients: a nationwide cohort study.

PURPOSE: Low muscle mass (LMM) is a risk factor for adverse health outcomes, but its prognostic relevance in cancer remains insufficiently studied. We investigated the independent and combined effects of LMM and obesity on mortality in cancer patients. METHODS: This cohort study included 635,867 cancer patients. LMM was defined as the lowest quartile on the appendicular skeletal muscle mass index (ASMI). Obesity was defined as body mass index ≥25 kg/m2 and abdominal obesity as waist circumference ≥90 cm (males) and ≥85 cm (females). Patients were classified into four groups based on muscle mass and obesity status. Cox proportional hazards models calculated adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for mortality. RESULTS: Compared with individuals in the highest ASMI quartile, LMM had significantly higher risks of all-cause (aHR 1.25, 95% CI 1.23-1.27), cancer-specific (aHR 1.21, 95% CI 1.19-1.23), cardiovascular (aHR 1.49, 95% CI 1.36-1.64), and respiratory mortality (aHR 2.26, 95% CI 1.99-2.56). While obesity was associated with lower mortality risks than non-obese status, the LMM with obesity group exhibited the highest risk for all-cause (aHR 1.22; 95% CI, 1.16-1.28) and cancer-specific mortality (aHR 1.22; 95% CI, 1.16-1.29). CONCLUSIONS: LMM was independently associated with increased mortality in cancer patients, regardless of obesity status. The adverse effect was amplified in those with both LMM and obesity, but obesity alone showed a modest inverse association. These findings highlight the clinical relevance of evaluating muscle mass and body composition in cancer.