Systemic Immune-Inflammation Index Predicts Overall Survival in Patients with Gastric Cancer: a Propensity Score–Matched Analysis

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Background
The systemic immune-inflammation index (SII), integrated by peripheral lymphocyte, neutrophil, and platelet counts, is used as an objective biomarker that reflects the balance between host inflammatory and immune response status in cancer patients. Herein, we examined the prognostic significance of SII in gastric cancer patients.

Methods
We retrospectively reviewed data of 415 patients who underwent curative laparoscopic gastrectomy using propensity score–matched (PSM) analysis. The prognostic value of SII was compared between two groups based on SII values: low SII group (SII < 661.9) and high SII group (SII ≥ 661.9).

Results
In multivariate analysis, the American Society of Anesthesiologists physical status (ASA-PS) (p < 0.001), tumor differentiation (p = 0.019), pathological stage (p = 0.046), carcinoembryonic antigen (CEA) level (p < 0.001), SII (p = 0.006), and operative procedure (p = 0.009) were independent prognostic factors of overall survival (OS) in the overall PSM cohort. The log-rank test demonstrated that patients with a high SII had significantly worse OS than did those with low SII (p = 0.002). In age-stratified subgroups analysis (< 65/≥ 65 years), multivariate analysis revealed that ASA-PS (p < 0.001), tumor differentiation (p = 0.019), CEA level (p = 0.008), SII (p = 0.013), and operative procedure (p = 0.026) were independent prognostic factors of OS in the elderly group. Similarly, elderly patients with a high SII had significantly worse OS than did those with a low SII (p = 0.009). Meanwhile, SII was not an independent prognostic factor of OS, and no significant association was observed between SII and OS in non-elderly patients.

Conclusions
SII was an independent prognostic indicator in gastric cancer patients, especially in the elderly population.