Association of IL-6 −174 G>C Polymorphism with Susceptibility to Colorectal Cancer and Gastric Cancer: a Systematic Review and Meta-Analysis

Background: The −174G>C (rs1800795) polymorphism at interleukin 6 (IL-6) gene has been reported to be related with the occurrence of colorectal (CRC) and gastric (GC) cancers. However, the results had been conflicting and controversial. In order to give a comprehensive and precise result, we summarized available data to analyze the association of this polymorphism with CRC and GC risk. Methods: A comprehensive literature search on PubMed, Elsevier Science Direct, and CNKI database was performed to identify all eligible studies up to May 15, 2019. The strength of association was assessed by odds ratios (ORs) with 95% confidence intervals (CI). Results: A total of 29 case-control studies including 16 studies with 7,560 cases and 9,574 controls on CRC and 13 studies with 1,445 cases and 2,918 controls on GC were selected. Overall, pooled data showed that the IL-6 −174G>C polymorphism was not significantly associated with increased risk of CRC and GC in overall. When stratified by ethnicity, we found a statistically significant association between the IL-6 −174 G>C polymorphism and CRC risk in Asians (CC vs. GG: OR = 1.860, 95% CI 1.061–3.258, p = 0.030; and CC vs. CG+GG: OR = 1.941, 95% CI 1.131–3.331, p = 0.016). Conclusion: The meta-analysis suggests that IL-6 −174G>C polymorphism was not significantly associated with the increased risk of CRC and GC in overall population. However, the results showed that IL-6 −174G>C polymorphism may be associated with risk of GC in Asians. Further studies including a larger sample size will be necessary to clarify these results.