Prognostic and clinicopathological significance of systemic immune-inflammation index in colorectal cancer: a meta-analysis

Previous studies on the systemic immune-inflammation index (SII), which is based on platelet, neutrophil and lymphocyte counts, as a prognostic marker in patients with colorectal cancer (CRC) yielded inconsistent results. The aim of this study was to evaluate the prognostic and clinicopathological role of SII in CRC via meta-analysis.A comprehensive literature survey was performed on PubMed, Web of Science, Embase and the Cochrane Library databases to include studies published up to 6 April 2020. Pooled hazard ratios (HRs) and odds ratios (ORs) with 95% confidence intervals (CIs) were computed to estimate the prognostic and clinicopathological value of SII in CRC.A total of 12 studies published between 2016 and 2019 were included in our meta-analysis. The combined analysis showed that high SII levels were significantly associated with worse overall survival (OS; HR = 1.61, 95% CI = 1.21-2.13, p = 0.001) and progression-free survival (HR = 1.74, 95% CI = 1.26-2.39, p = 0.001) in CRC. Moreover, elevated SII was also correlated with poor tumor differentiation (OR = 1.60, 95% CI = 1.27-2.02, p < 0.001), presence of distant metastasis (OR = 2.27, 95% CI = 1.10-4.67, p = 0.026), ECOG PS of 1-2 (OR = 1.98, 95% CI = 1.39-2.84, p < 0.001) and tumor size ⩾5 cm (OR = 1.49, 95% CI = 1.18-1.88, p = 0.001). However, high SII was not significantly associated with sex, tumor location, lymph node metastasis, or age in patients with CRC.Our meta-analysis indicated that high SII levels predicted poor prognosis in CRC. In addition, an elevated SII was also associated with clinical factors, implying higher malignancy of the disease.