Prognostic value of the systemic immune-inflammation index in gastrointestinal cancers treated with immune checkpoint inhibitors: a systematic review and meta-analysis

Gastrointestinal (GI) cancers, including pancreatic, gastric, esophageal, colorectal, and hepatocellular carcinoma (HCC), have high mortality rates. Despite advances in immune checkpoint inhibitors (ICIs), treatment outcomes remain variable. Identifying reliable biomarkers, such as the systemic immune-inflammation index (SII), which combines platelet, neutrophil, and lymphocyte counts, could help optimize treatment strategies. Biologically, an elevated SII is thought to indicate a dominance of pro-tumor inflammation and a suppressed adaptive immune response, thereby potentially dampening the therapeutic efficacy of ICIs. A systematic review was conducted of studies from Cochrane Library, Embase, and PubMed, published until August 15, 2025. This review was conducted in strict adherence to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Eligible studies involved GI cancer patients treated with ICIs, reported baseline or treatment SII data, and provided hazard ratios (HRs) for progression-free survival (PFS) or overall survival (OS). Exclusions included studies on non-GI cancers or incomplete data. 28 studies with 4752 patients were included. High baseline SII levels were associated with worse OS and PFS in gastric cancer (OS: HR = 2.24, 95% CI: 1.84–2.72, I 2 = 19.4%; PFS: HR = 1.57, 95% CI: 1.35–1.83, I 2 = 0%), HCC (OS: HR = 1.80, 95% CI: 1.47–2.21, I 2 = 2.6%; PFS: HR = 1.60, 95% CI: 1.24–2.06, I 2 = 53.7%), and esophageal cancer (OS: HR = 1.79, 95% CI: 1.53–2.09, I 2 = 39.8%; PFS: HR = 1.50, 95% CI: 1.12–2.01, I 2 = 32.6%). Baseline SII was a stronger predictor of survival than post-treatment or dynamic measurements. SII is a promising, cost-effective prognostic biomarker for GI cancer patients receiving ICIs. Elevated baseline SII predicts poorer survival, particularly in gastric cancer, HCC, and esophageal cancer. These findings highlight the potential utility of SII in patient risk stratification and clinical decision-making, thereby supporting its integration into precision oncology strategies.