Passive Smoking and Risk of Colorectal Cancer: A Meta-analysis of Observational Studies.

We conducted this meta-analysis to explore the association between passive smoking and the risk of colorectal cancer. A literature search of online databases, including MEDLINE, EMBASE, the Cochrane Library, and Web of Science was performed up to June 30, 2015. A fixed-effects meta-analysis using Stata 12.0 was carried out to estimate the relative risks (RRs) and 95% confidence intervals (CIs) for the associations. Eleven articles, including 6 case-control studies and 6 cohort studies, were included in our analysis according to inclusion and exclusion criteria. The pooled RR of all studies showed a statistically significant association between passive smoking and colorectal cancer (RR = 1.14; 95% CI = 1.05-1.24). Results of subgroup analysis showed a positive association between passive smoking and rectal cancer ((RR = 1.33; 95% CI = 1.15-1.53) and that male passive smokers were at greater risks of colorectal cancer (RR = 1.73; 95% CI = 1.37-2.19) than females. Results suggested that passive smoking is associated with an increased risk of colorectal cancer.