SYSTEMIC IMMUNE INFLAMMATION INDEX AS A PROGNOSTIC MARKER IN COLORECTAL CANCER

Abstract

Elevated preoperative Systemic Immune-Inflammation Index (SII), calculated as platelet count × neutrophil count ÷ lymphocyte count, was evaluated as a prognostic biomarker in a prospective cohort of 200 colorectal cancer patients undergoing curative resection between January 2022 and December 2023. Using ROC-derived thresholds for 2-year overall survival, patients were stratified into low- and high-SII groups and followed for a median of 36 months. High SII was significantly associated with advanced TNM stage (III–IV: 62% vs. 45%, p = 0.012), increased lymphovascular invasion (48% vs. 28%, p = 0.003), and elevated carcinoembryonic antigen (>5 ng/mL: 40% vs. 22%, p = 0.001). Kaplan–Meier analysis revealed markedly reduced overall and disease-free survival in the high-SII group (both log-rank p < 0.001). Multivariable Cox regression, adjusting for age, sex, stage, and adjuvant therapy, confirmed high SII as an independent predictor of poorer overall survival (hazard ratio 1.84, 95% CI 1.21–2.79, p = 0.004). Additionally, high-SII patients demonstrated lower complete response rates to standard adjuvant chemotherapy (28% vs. 45%, p = 0.008). These findings indicate that preoperative SII, readily obtainable from routine blood counts, provides cost-effective, independent prognostic information and may enhance risk stratification and therapeutic decision-making in colorectal cancer management.