Smoking and risk of cholangiocarcinoma: a systematic review and meta-analysis

// Yuenan Huang 1, * , Liuping You 1, * , Weimin Xie 2, * , Li Ning 2, * and Jinghe Lang 2 1 Department of General Surgery, The Second Affiliated Hospital, Harbin Medical University, Harbin, China 2 Department of Obstetrics and Gynecology, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China * These authors contributed equally to this work Correspondence to: Yuenan Huang, email: dr-huangyuenan@163.com Keywords: smoking, cholangiocarcinoma, risk, meta-analysis Received: May 01, 2017      Accepted: July 30, 2017      Published: August 10, 2017 ABSTRACT Previous studies evaluating the association between smoking and risk of cholangiocarcinoma (CCA) have yielded controversial results. We conducted a meta-analysis to evaluate the association based on available evidence. We searched the databases of Embase, PubMed and Cochrane Central Register of Controlled Trials from inception to April 11, 2017. Studies that investigated the association between smoking and risk of CCA were included. Pooled odds ratio (OR) estimates and 95% confidence intervals (CIs) were calculated using either a random-effects or a fixed-effects model. A total of 22 studies involving 324,333 participants were identified. The summary OR of CCA was 1.31 (95% CI, 1.15 to 1.51) for smokers versus nonsmokers. The increased risk was independent of diabetes mellitus, bilious tract stone disease, and liver cirrhosis. Smokers also had increased risk of intrahepatic CCA (12 studies; OR, 1.31; 95% CI, 1.06 to 1.63) and extrahepatic CCA (12 studies; OR, 1.32; 95% CI, 1.10 to 1.59) compared with nonsmokers. The results of our meta-analysis support the hypothesis that there is a moderate association between cigarette smoking and risk of CCA.