Hepatitis B infection is causally associated with extrahepatic cancers: a Mendelian randomization study

Overwhelming evidence suggests that chronic hepatitis infection is associated with extrahepatic cancers. However, uncertainties exist about this association as much of the current evidence evolve from observational studies which are susceptible to confounding. We performed two-sample Mendelian randomization (MR) to explore the causal associations between chronic hepatitis infection and extrahepatic cancers. Genetic variants associated with chronic hepatitis B virus (HBV) infection and chronic hepatitis C virus (HCV) infection were identified from a large genome-wide association study. Summary level data for cancer of the biliary tract, cervix, colorectum, endometrium, esophagus, gastric, liver, lung, ovary and pancreas were obtained from the Biobank Japan. Using the inverse variance weighted method, we found chronic HBV infection to be causally associated with gastric cancer (odds ratio [OR] = 1.19 and 95% confidence interval [CI] = 1.13-1.25, P-value = 0.001) and lung cancer (OR = 1.21, 95% CI = 1.14-1.28, P-value = 0.001). Moreover, chronic HBV infection (OR = 1.34, 95% CI = 1.17-1.53, P-value = 0.007) and chronic HCV infection (OR = 2.75, 95% CI = 2.21-3.42, P-value = 0.0008) were all causally associated with liver cancer, supporting a well-established association between chronic hepatitis infection and liver cancer. In conclusions, our MR findings revealed that chronic HBV infection is causally associated with extrahepatic cancers including gastric and lung cancers.