The systemic immune-inflammation index predicts prognosis in intrahepatic cholangiocarcinoma: an international multi-institutional analysis

Background: The objective of this study was to examine whether the systemic immune inflammation index (SII) was associated with prognosis among patients following resection of intrahepatic cholangiocarcinoma (ICC). Methods: The impact of SII on overall (OS) and cancer-specific survival (CSS) following resection of ICC was assessed. The performance of the final multivariable models that incorporated inflammatory markers (i.e. neutrophil-to-lymphocyte ratio [NLR], platelet-to-lymphocyte ratio [PLR] and SII [platelets∗NLR]) was assessed using the Harrell's concordance index. Results: Patients with high SII had worse 5-year OS (37.7% vs 46.6%, p < 0.001) and CSS (46.1% vs 50.1%, p < 0.001) compared with patients with low SII. An elevated SII (HR = 1.70, 95% CI 1.23–2.34) and NLR (HR = 1.58, 95% CI 1.10–2.27) independently predicted worse OS, whereas high PLR (HR = 1.17, 95% CI 0.85–1.60) was no longer associated with prognosis. Only SII remained an independent predictor of CSS (HR = 1.55, 95% CI 1.09–2.21). The SII multivariable model outperformed models that incorporated PLR and NLR relative to OS (c-index; 0.696 vs 0.689 vs 0.692) and CSS (c-index; 0.697 vs 0.689 vs 0.690). Conclusion: SII independently predicted OS and CSS among patients with resectable ICC. SII may be a better predictor of outcomes compared with other markers of inflammatory response among patients with resectable ICC.