The Prognostic Role of Systemic Inflammatory Response Index in Surgically Treated Pancreatic Ductal Adenocarcinoma Patients

Background: Pancreatic ductal adenocarcinoma (PDAC) remains a highly lethal malignancy despite advances in treatment. The systemic inflammatory response index (SIRI), a composite marker of neutrophils, monocytes, and lymphocytes, has been proposed as a prognostic biomarker in various cancers. However, its role in resectable PDAC is not well established. Methods: This retrospective study analyzed 82 patients who underwent curative-intent surgery for PDAC between 2011 and 2021. Preoperative SIRI was calculated as (neutrophils × monocytes) / lymphocytes using blood counts obtained within one week before surgery. The optimal SIRI cut-off for overall survival (OS) prediction was determined using ROC analysis. Survival outcomes were assessed via Kaplan-Meier curves and Cox regression models. Results: The optimal SIRI cut-off was 1.36 (AUC: 0.738). Patients with SIRI ≤1.36 had significantly longer OS than those with SIRI >1.36 (42 vs. 22 months, p=0.013), including among early-stage patients. In multivariate analysis, SIRI >1.36 remained an independent predictor of poor OS (HR: 1.87, 95% CI: 1.08–3.21, p=0.023), along with age, ECOG status, and disease stage. Conclusions: Preoperative SIRI is an independent prognostic marker in resectable PDAC and may help identify high-risk patients who could benefit from intensified follow-up or additional therapeutic strategies. Prospective multicenter studies are warranted to validate these findings and integrate SIRI into clinical risk models.