The Global Immune–Nutrition–Inflammation Index Is Associated with Survival Outcomes and Enhances Prognostic Discrimination in Metastatic Pancreatic Cancer

Background and Objectives: Metastatic pancreatic ductal adenocarcinoma (PDAC) continues to carry a poor prognosis despite advances in treatment, underscoring the need for simple and accessible biomarkers that reflect tumor–host interactions. The Global Immune–Nutrition–Inflammation Index (GINI), which combines inflammatory, immune, and nutritional parameters, may offer improved prognostic stratification compared with conventional indices. Materials and Methods: This retrospective cohort study included 126 patients with metastatic PDAC treated between 2015 and 2024. GINI, neutrophil-to-lymphocyte ratio (NLR), systemic immune-inflammation index (SII), and systemic inflammation response index (SIRI) were calculated using baseline laboratory data. Discriminative ability was evaluated by receiver operating characteristic (ROC) analysis. Survival outcomes were assessed using Kaplan–Meier curves and Cox proportional hazards models. Results: Among the evaluated indices, GINI showed the best discriminative performance (AUC, 0.769; 95% CI, 0.637–0.900), with a sensitivity of 78.8% and specificity of 76.9%. Patients with lower GINI values had significantly longer overall survival than those with higher values (median OS, 11.0 vs. 7.0 months; p = 0.014). Although progression-free survival differed statistically (p = 0.006), median PFS was the same in both groups (5.0 months). In univariable analysis, higher GINI was associated with worse OS (HR, 1.67; p = 0.022) and PFS (HR, 1.75; p = 0.012). However, in multivariable analysis, ECOG performance status remained the only consistent independent predictor, and GINI was no longer significant. Conclusions: GINI is a practical and biologically meaningful biomarker that improves risk discrimination in metastatic PDAC. While it does not retain independent prognostic significance, its ability to capture the overall tumor–host interaction  supports its use as a complementary tool for baseline risk assessment.