J Natl Cancer Inst 2019 May 24. Epub 2019 May 24.
Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, MD, USA.
Background: Tobacco and alcohol are well-established risk factors for numerous cancers, yet their relationship to biliary tract cancers remains unclear.
Methods: We pooled data from 26 prospective studies to evaluate associations of cigarette smoking and alcohol consumption with biliary tract cancer risk. Study-specific hazard ratios (HRs) and 95% confidence intervals (CIs) for associations with smoking and alcohol consumption were calculated. Random effects meta-analysis produced summary estimates. All statistical tests were two-sided.
Results: Over a period of 38,369,156 person-years of follow-up, 1,391 gallbladder, 758 intrahepatic bile duct, 1,208 extrahepatic bile duct, and 623 ampulla of Vater cancer cases were identified. Ever, former, and current smoking were associated with increased extrahepatic bile duct and ampulla of Vater cancers risk (e.g., current versus never smokers hazard ratio [HR] = 1.69, 95% confidence interval [CI] = 1.34 to 2.13 and 2.22, 95%CI = 1.69 to 2.92, respectively), with dose-response effects for smoking pack-years, duration, and intensity (all P-trend<0.01). Current smoking and smoking intensity were also associated with intrahepatic bile duct cancer (e.g., >40 cigarettes/day versus never smokers HR = 2.15, 95%CI: 1.15 to 4.00; P-trend=0.001). No convincing association was observed between smoking and gallbladder cancer. Alcohol consumption was only associated with intrahepatic bile duct cancer, with increased risk for individuals consuming ≥5 versus 0 drinks/day (HR = 2.35, 95%CI = 1.46 to 3.78; P-trend=0.04). There was evidence of statistical heterogeneity between several cancer sites, particularly between gallbladder cancer and the other biliary tract cancers.
Conclusions: Smoking appears to increase the risk of developing all biliary tract cancers except gallbladder cancer. Alcohol may increase the risk of intrahepatic bile duct cancer. Findings highlight etiologic heterogeneity across the biliary tract.