Systemic immune-inflammation index predicts prognosis and responsiveness to immunotherapy in cancer patients: a systematic review and meta‑analysis

The systemic immune-inflammation index (SII) is a significant prognostic factor in some cancer types. However, the prognostic role of SII in cancer patients with immunotherapy remains uncertain. We aimed to evaluate the relationship between pretreatment SII and clinical survival outcomes for advanced-stage cancer patients treated with immune checkpoint inhibitors (ICIs). A comprehensive literature search was performed to identify eligible studies concerning the association between pretreatment SII and survival outcomes in advanced cancer patients treated with ICIs. The data were extracted from publications and used to calculate the pooled odds ratio (pOR) for objective response rate (ORR), disease control rate (DCR), and pooled hazard ratio (pHR) for overall survival (OS), progressive-free survival (PFS), along with 95% confidence intervals (95% CIs). Fifteen articles with 2438 participants were included. A higher level of SII indicated a lower ORR (pOR = 0.73, 95% CI 0.56-0.94) and worse DCR (pOR = 0.56, 95% CI 0.35-0.88). High SII was associated with a shorter OS (pHR = 2.33, 95% CI 2.02-2.69) and unfavorable PFS (pHR = 1.85, 95% CI 1.61-2.14). Therefore, high SII level might be a non-invasive and efficacious biomarker of poor tumor response and adverse prognosis of advanced cancer patients with immunotherapy.