Published online Dec 14, 2013. doi: 10.3748/wjg.v19.i46.8780
Revised: October 4, 2013
Accepted: October 13, 2013
Published online: December 14, 2013
Processing time: 126 Days and 10.8 Hours
AIM: To assess the association between smoking and alcohol consumption and extrahepatic cholangiocarcinoma (ECC) through a meta-analysis of clinical observational studies.
METHODS: A literature search was conducted using Embase and MEDLINE databases from inception to 31 May 2013 without language limitations, and by manually searching the references of retrieved articles. Case-control and cohort studies that investigated the association between smoking or alcohol consumption and ECC were included. The quality of these studies was assessed using the Newcastle-Ottawa quality assessment scale. Summary relative risks and corresponding 95%CI were calculated using a random-effects model. Publication bias was assessed by Begg’s funnel plot and Egger’s test.
RESULTS: A total of 12 eligible articles (11 case-control studies and one cohort study) were included in this meta-analysis. Eleven studies reported the association between smoking and ECC. Pooled analysis indicated that smokers had an increased risk of ECC development as compared with non-smokers (summary RR = 1.23; 95%CI: 1.01-1.50). This correlation was present in population-based studies (n = 5; summary RR = 1.47; 95%CI: 1.06-2.05) but not in hospital-based studies (n = 6; summary RR = 1.10; 95%CI: 0.88-1.37) and in non-Asian regions (n = 7; summary RR = 1.39; 95%CI: 1.03-1.87) but not in Asia (n = 4; summary RR = 1.08; 95%CI: 0.85-1.38). Seven studies reported an association between consuming alcohol and ECC. Pooled analysis indicated that alcohol drinkers had a similar risk of ECC development as did individuals who did not drink alcohol (summary RR = 1.09; 95%CI: 0.87-1.37). There was moderate heterogeneity among the studies and no evidence of publication bias.
CONCLUSION: Smoking is associated with an increased risk of ECC, but alcohol consumption is not. Further population-based studies, particularly cohort studies, are warranted to enable definitive conclusions.
Core tip: Little is known about the etiology of extrahepatic cholangiocarcinoma (ECC) because of its rarity and high fatality. Smoking and alcohol consumption are potential risk factors for ECC development. However, reported relations between these two risk factors and ECC are conflicting. Our meta-analysis identified a positive association between smoking and the risk of ECC. The association between alcohol consumption and the risk of ECC was positive but not significant. Further investigations are required.