The Value of the Systemic Immune-Inflammation Index in Predicting Survival Outcomes in Patients with Brain Metastases of Non-Small-Cell Lung Cancer Treated with Stereotactic Radiotherapy

BACKGROUND: As a parameter integrating platelet (P), neutrophil (N), and lymphocyte (L) levels, the systemic immune-inflammation index (SII) has been used as a prognostic marker for patient survival in various types of solid malignant tumors. However, there is no in-depth study in non-small-cell lung cancer (NSCLC) patients with brain metastases after stereotactic radiotherapy. Therefore, we performed a retrospective analysis to determine the clinical and prognostic value of the SII in NSCLC patients with brain metastases who underwent stereotactic radiotherapy. MATERIALS AND METHODS: We enrolled 124 NSCLC patients with brain metastases treated with stereotactic radiotherapy in our hospital between May 2015 and June 2018. We obtained all baseline blood samples within one week prior to stereotactic radiotherapy. The SII was calculated by the following formula: neutrophil counts × platelet counts/lymphocyte counts. The optimal cutoff value of the SII for predicting prognosis was assessed by receiver operating characteristic (ROC) curves with the maximum log-rank values. The discriminative ability of predicting prognosis was calculated and compared using the Kaplan–Meier method and log-rank test. The hazard ratio (HR) and 95% confidence interval (CI) were combined to evaluate the prognostic impact of the blood index on overall survival (OS) and progression-free survival (PFS). Only those parameters that proved to be associated with statistically significant differences in clinical outcomes were compared in multivariate analysis using a multiple Cox proportional hazard regression model to identify independent prognostic factors. RESULTS: Of the total enrolled patients, 53.2% and 46.8% have high SII and low SII, respectively. In this study, Kaplan–Meier curve analysis revealed that the median PFS was 9 months (range: 2–22 months) and the median OS was 18 months (range: 4–37 months). Applying an optimal cutoff of 480 (SII), the median PFS was better in the low SII group patients (11.5 vs. 9 months), and the median OS was significantly longer in the low SII group patients (20 vs. 18 months). A SII > 480 was significantly associated with worse OS (HR: 2.196; 95% CI 1.259–3.832; P = 0.006) and PFS (HR: 2.471; 95% CI 1.488–4.104; P < 0.001) according to univariate analysis. In multivariate analysis, only age (HR: 2.159; 95% CI 1.205–3.869; P = 0.010), KPS (HR: 1.887; 95% CI 1.114–3.198; P = 0.018), and SII (HR: 1.938; 95% CI 1.046–3.589; P = 0.035) were independently correlated with OS, and SII (HR: 2.224; 95% CI 1.298–3.810; P = 0.004) was an independent prognostic predictor of PFS, whereas we found that other inflammation-based indices lost their independent value. CONCLUSIONS: The SII, which is an integrated blood parameter based on platelet, neutrophil, and lymphocyte counts, may be an independent prognostic indicator and may be useful for the identification of NSCLC patients with brain metastases after stereotactic radiotherapy at high risk for recurrence.