Systemic immune-inflammation index is a stage-dependent prognostic factor in patients with operable non-small cell lung cancer

BACKGROUND: Immune function is a key component affecting tumor progression in patients with cancer. The purpose of this study was to identify the prognostic value of systemic immune-inflammation index (SII) in patients with non-small cell lung cancer (NSCLC) and the differences of its prognostic value in patients with distinct characteristics. METHODS: Patients with completely resected NSCLC were reviewed according to the eighth TNM classification of lung cancer. Patients were further categorized into the low- and high-SII groups. Cox proportional hazard analyses were performed to identify the independent prognostic factors. RESULTS: A total of 3984 patients with NSCLC were enrolled in this study. Kaplan-Meier analyses demonstrated that high SII was associated with worse recurrence-free survival (RFS) (P<0.001) and overall survival (OS) (P<0.001). Cox proportional hazard analyses revealed that SII was an independent risk factor for worse RFS (P=0.038) and OS (P=0.043). Further analyses demonstrated that the prognostic value of SII was observed only in patients with stage I disease (P<0.001), solid nodules (P=0.002), or adenocarcinoma (P<0.001). Sensitivity analyses using multiple imputation and competing risk analyses also confirmed similar results. CONCLUSIONS: SII was associated with worse survival independently, and its prognostic role was exhibited solely in NSCLC patients with stage I disease, solid nodules, and adenocarcinoma. This study helped us specify the target population for clinical use of SII.