High Systemic Immune-Inflammation Index (SII) Represents an Unfavorable Prognostic Factor for Small Cell Lung Cancer Treated with Etoposide and Platinum-Based Chemotherapy

Systemic immune-inflammation index (SII) has been demonstrated to be closely associated with prognosis of a series of solid tumors. However, its role in small cell lung cancer (SCLC) remains poorly understood. The present study aims to evaluate the prognostic significance of pretreatment SII in SCLC treated with etoposide and platinum-based chemotherapy.

Sixty hundred and fifty-three newly diagnosed SCLC patients were enrolled. The optimal cut-off values for SII and LDH (lactate dehydrogenase) were obtained by a receiver operating characteristic (ROC) curve analysis. Overall survival (OS) was assessed by univariate and multivariate analyses.

The optimal cut-off values of pretreatment SII and LDH were 748.51 × 10⁹/L and 188.5 U/L, respectively. High pretreatment SII was significantly associated with advanced tumor stage (limited disease, LD vs. extensive disease, ED; 26.3% vs 46.5%; p < 0.001). On univariate analysis, age < 65 years, female, non-smoker, limited disease, SII < 748.51 × 10⁹/L, LDH < 188.5 U/L, distant metastasis numbers < 2, chemotherapy + radiotherapy, and chemotherapy + surgery were closely correlated with a prolonged OS (p < 0.05). The median OS for patients in high SII group was 12.0 months, compared with that of 17.0 months for patients in low SII group. Multivariate analysis showed smoking history (p = 0.014), tumor stage (p < 0.001), pretreatment SII (p < 0.001), LDH (p = 0.002), distant metastasis numbers (p = 0.006), and chemotherapy + radiotherapy (p < 0.001) were independent prognostic factors of OS. Furthermore, SII remained prognostic significance for SCLC stratified by variable subgroups analysis.

Pretreatment SII represents a powerful prognostic biomarker for SCLC patients treated with etoposide and platinum-based chemotherapy. It is significant for treatment strategy making in clinics.