A Cohort Study on Systemic Immune-Inflammation Index and Its Longitudinal Change in Relation to Colorectal Adenoma Recurrence

Objective: This study aimed to investigate the associations of both baseline systemic immune-inflammation index (SII) and, more importantly, its longitudinal change (ΔSII) during follow-up with the risk of advanced colorectal neoplasia (ACRN) recurrence after endoscopic resection of colorectal adenomas. Methods: Clinical data from 1855 patients diagnosed with colorectal adenomas and undergoing resection at Hospital between January 2017 and August 2023 were analyzed. Patients were classified into Q1–Q4 groups based on baseline SII quartiles and into three groups according to ΔSII. Cox proportional hazards regression models, restricted cubic spline (RCS) analysis, Kaplan-Meier curves, receiver operating characteristic (ROC) curve, subgroup analysis, sensitivity analyses were used to evaluate associations. Results: After an average follow-up of 3.4 years, 166 patients (8.95%) experienced ACRN recurrence. After fully adjusting for variables, Cox proportional hazards regression analysis revealed that the group with the highest baseline SII (Q4) had a 1.75-fold increased risk of ACRN recurrence compared to Q1 (HR, 1.75; 95% CI , 1.12– 2.75). Patients with a significant SII increase (ΔSII > 0.15) had a 1.88-fold higher recurrence risk than those with a stable SII (− 0.15 ≤ ΔSII ≤ 0.15) (HR, 1.88; 95% CI , 1.24– 2.86). Dose-response curves indicated a rising ACRN recurrence risk when ΔSII ranged from 0.008 to 1.103, followed by a declining trend for ΔSII ≥ 1.103 ( P -overall=0.003, P -nonlinear=0.005). ROC analysis showed that incorporating either SII levels or ΔSII grouping improved the predictive ability (AUC) for postoperative recurrence. Subgroup analyses confirmed that both a high baseline SII (Q4) and a significant SII increase (ΔSII > 0.15) were associated with elevated recurrence risk, particularly among males and older adults. Conclusion: Not only baseline SII but also ΔSII during follow-up serves as a significant and independent predictor for ACRN recurrence. Monitoring the longitudinal change of SII may provide incremental clinical value for optimizing personalized surveillance strategies after endoscopic resection. Keywords: systemic immune-inflammation index, colorectal cancer, advanced colorectal neoplasia, recurrence, cohort study