Purpose: Many studies have evaluated the associations between pre-diagnostic circulating C-reactive protein (CRP), interleukin-6 (IL-6) and colorectal cancer risk, but their results are inconsistent. We therefore conducted a meta-analysis to investigate these associations.
Methods: A comprehensive literature search up to October 2013 was undertaken in PubMed. Pooled relative risk (RR) estimates and 95% confidence intervals (CIs) were used to calculate estimated effect.
Results: Eighteen studies on CRP comprising a total of 4,706 colorectal cancer cases were included in this meta-analysis. The summary RR of colorectal cancer for one unit change in natural logarithm (ln) CRP was 1.12 [95% CI (1.05-1.21)]. There was statistically significant heterogeneity among studies (p = 0.006; I (2) = 51.7%). After excluding the studies contributing most to the heterogeneity, summary estimate was essentially unchanged. In addition, the association was significant for colon cancer [RR = 1.13, 95 % CI (1.05-1.21)], not for rectal cancer [RR = 1.03, 95% CI (0.90-1.17)]. We also found that CRP was significantly associated with increased risk of colorectal cancer among men, but not among women. There were six studies on IL-6 that involved a total of 1,068 colorectal cancer cases. The pooled RR of colorectal cancer for one unit change in ln IL-6 was 1.10 (95% CI 0.88-1.36), and no statistically significant heterogeneity was found (p = 0.175; I(2) = 34.8%).
Conclusion: Our results suggest that pre-diagnostic circulating CRP is associated with increased risk of colorectal cancer. However, there is no significant association between IL-6 and colorectal cancer risk.