Significance of a preoperative systemic immune-inflammation index as a predictor of postoperative survival outcomes in gastric cancer

BACKGROUND: Since inflammation and the immune system contribute to the development and progression of malignancies, parameters that reflect a host’s immune-inflammatory status may be useful prognostic indicators of gastric cancer (GC). The present study examined the clinical significance of a preoperative systemic immune-inflammation index (SII) for predicting postoperative survival outcomes in GC. METHODS: A total of 447 patients who underwent curative gastrectomy for GC were included in the present study. SII was calculated as platelet count × neutrophil count/lymphocyte count. The prognostic impact of preoperative SII was examined using univariate and multivariate analyses. RESULTS: Preoperative SII ranged between 105 and 4455 (median 474), and the optimal cutoff value for predicting overall survival (OS) was 395 based on a receiver operating characteristic curve. The 5-year OS rate of the SII ≥ 395 group was 80.0%, which was significantly worse than that (92.7%) of the SII < 395 group (p < 0.001). The multivariate analysis identified SII ≥ 395 (hazard ratio [HR] 2.95; 95% confidence interval [CI] 1.49–6.39; p = 0.001), heart disease (HR 2.14, 95% CI 1.07–4.07), C-reactive protein ≥ 0.5 (HR 2.45, 95% CI 1.15–4.94), pT4 (HR 4.46, 95% CI 2.44–8.14), and pN+ (HR 4.02, 95% CI 2.10–7.93) as independent predictors of worse OS. Peritoneal recurrence was more frequent in the high SII group than in the low SII group (p = 0.028). CONCLUSION: Preoperative SII may be a useful predictor of postoperative survival outcomes in GC. The meticulous surveillance of GC relapse, particularly peritoneal dissemination, is necessary for patients with SII ≥ 395 even after curative gastrectomy. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12957-021-02286-3.