Postoperative Geriatric Nutritional Risk Index as a Determinant of Tolerance to S-1 Adjuvant Chemotherapy After Curative Surgery for Pancreatic Ductal Adenocarcinoma: A Cohort Study with External Validation

S-1 adjuvant chemotherapy (AC) is the standard treatment for pancreatic ductal adenocarcinoma (PDAC) after curative surgery in Japan. Our prior research suggested that a lower postoperative geriatric nutritional risk index (GNRI) predicts S-1 discontinuation due to adverse events (AEs). This study aimed to validate the GNRI as a predictor of S-1 non-completion using an independent cohort. <b>Methods:</b> This retrospective study analyzed 180 patients who underwent curative PDAC resection at Dokkyo Medical University from January 2010 to March 2023. Postoperative GNRI values were recorded as part of nutritional screening. Data on S-1 therapy completion and related clinical factors were analyzed statistically. <b>Results:</b> Patients were classified based on S-1 completion (<i>N</i> = 93) and non-completion (<i>N</i> = 48). GNRI values were significantly lower in the non-completion group. A GNRI threshold of 94.4, identified in a prior study, effectively distinguished patients at risk of discontinuation. Univariate analysis confirmed that a GNRI of ≥94.4 was a significant predictor of successful S-1 completion [hazard ratio (HR) for recurrence-free survival (RFS), 1.54; 95% confidence interval (CI) 1.04-2.28 and for overall survival (OS), 1.89; 95% CI 1.20-2.99]. <b>Conclusions:</b> This study validated previous findings, confirming that the postoperative GNRI reliably identifies patients at risk of S-1 non-completion due to AEs after PDAC surgery. The GNRI serves as a practical marker for optimizing patient care and enhancing AC efficacy.