The effect of smoking on the risk of gallbladder cancer: a meta-analysis of observational studies

BACKGROUNDCigarette smoking has been shown to cause many nonpulmonary cancers, including those of liver, pancreas and bladder. However, results of epidemiologic studies examining the association between smoking and gallbladder cancer (GBC) have been mixed. To clarify the association of cigarette smoking and GBC, we performed a meta-analysis of observational studies. METHODSA literature search was performed using Medline (from 1 January 1966) and Embase (from 1 January 1974), through 31 January 2012, and by manually searching the reference lists of pertinent articles. Summary relative risks (SRRs) with corresponding 95% confidence intervals (CIs) were calculated with a random-effects model. RESULTSA total of 11 articles (10 case–control and one prospective cohort studies) were used in this meta-analysis, which is based on a total of 1178 GBC cases. Analysis of 11 studies found that smokers had an increased risk of GBC development, compared with nonsmokers (SRRs 1.45, 95% CIs, 1.11–1.89). There was moderate heterogeneity among studies (Q=18.15, P=0.052, I =44.9%). These increased risks were independent of alcohol use and a history of gallstones. No significant publication bias was found. CONCLUSIONAlthough the current evidence supports a positive link between cigarette smoking and risk of gallbladder cancer, additional population-based studies, particularly cohort studies, are needed before definitive conclusions can be drawn.