The systemic immune-inflammation index is an independent predictor of survival for metastatic colorectal cancer and its association with the lymphocytic response to the tumor

BACKGROUND: Systemic inflammation and immune dysfunction has been proved to be significantly associated with cancer progression and metastasis in many cancer types, including colorectal cancer. We examined the prognostic significance of the systemic immune-inflammation index (SII) in patients with metastatic colorectal cancer (mCRC) and the relationship between the lymphocytic response to the tumor and this index. METHODS: This retrospective study evaluated 240 consecutive patients with newly diagnosed stage IV mCRC who underwent surgical resection. The SII values were calculated based on preoperative laboratory data regarding platelet, neutrophil, and lymphocyte counts. Tumor-infiltrating lymphocytes were evaluated using the surgical specimens. The overall survival and their 95% confidence interval (95% CI) were estimated by regression analyses and the Kaplan–Meier method. RESULTS: After a mean follow-up of 26.7 (1.1–92.4) months, 146 patients (60.8%) died. In the univariate analysis, a high SII was significantly associated with poor overall survival (P = 0.009). The multivariable analysis also confirmed that a high SII was independently associated with poor overall survival (hazard ratio: 1.462, 95% confidence interval 1.049–2.038, P = 0.025). The SII value was significantly correlated with the TILs value at the tumor’s center (P = 0.04), but not at the invasive margin (P = 0.39). When we evaluated overall survival for groupings of the tumor-infiltrating lymphocytes and SII values, we identified three distinct prognostic groups. The group with low tumor-infiltrating lymphocyte values and high SII values had the worst prognosis. CONCLUSIONS: A high SII value independently predicts poor clinical outcomes among patients with mCRC. In addition, combining the lymphocytic response to the tumor and SII could further enhance prognostication for mCRC. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12967-018-1638-9) contains supplementary material, which is available to authorized users.