Bioelectrical Impedance Analysis-Derived Water Composition Ratios Predict Survival Outcomes in Gastric Cancer: A Multicenter Cohort Study

Bioelectrical impedance analysis (BIA)-derived water composition ratios are non-invasive and cost-effective indices that reflect body fluid distribution. This study aimed to investigate the associations between these BIA-derived ratios and overall survival (OS) in patients with gastric cancer. A retrospective multicenter study included 385 gastric cancer patients. Optimal cutoffs were determined via Receiver Operating Characteristic (ROC) curves. Kaplan-Meier survival analysis, Cox regression analysis, and restricted cubic spline (RCS) evaluated associations with OS. The optimal cutoff values were 0.389 for extracellular water (ECW)/total body water (TBW), 0.611 for intracellular water (ICW]/TBW, and 0.638 for ECW/ICW. Kaplan-Meier survival analysis revealed that elevated ECW/TBW (72.6% vs. 58.7%; p<0.001) and ECW/ICW (59.1% vs. 72.4%; p<0.001) were associated with poorer OS, while a higher ICW/TBW (73.4% vs. 57.3%; p<0.001) indicated better prognosis. In RCS models, ECW/TBW (HR=1.552, 1.202-2.005, p=0.001) and ECW/ICW (HR=1.735, 1.320-2.280, p<0.001) independently predicted worse OS, whereas ICW/TBW inversely correlated with mortality (HR=0.620, 0.486-0.790, p<0.001). Multivariable Cox regression analysis further confirmed that higher ECW/TBW (HR=1.552, 95% CI 1.272-2.688, p<0.001) and ECW/ICW (HR=1.735, 1.320-2.280, p<0.001) ratios independently predicted worse OS. Conversely, a higher ICW/TBW ratio was inversely correlated with mortality (HR=0.567, 95% CI 0.390-0.824, p=0.003). The ECW/ICW ratio demonstrated the highest C-index (0.596), outperforming other ratios in predicting survival. These associations were consistent across subgroups, including advanced-stage patients. BIA-derived water composition ratios, particularly ECW/ICW, are robust and independent predictors of survival in gastric cancer patients, reflecting underlying metabolic and inflammatory disturbances. These non-invasive and cost-effective markers could enhance prognostic accuracy and guide personalized treatment strategies.