Cancer risk and survival according to body mass index in hepatobiliary malignancies: a nationwide registry-based cohort study.

BACKGROUND: The aim of this study was to explore the associations between BMI and cancer of the liver, bile ducts, and gallbladder. METHODS: A registry-based cohort study was performed by linking data from several national registries in Norway. RESULTS: The cohort comprised 1 723 692 individuals including 4768 hepatobiliary cancer cases during 55 743 509 person-years of follow-up. In men, we found increased risk of cancer per 5 kg/m2 BMI increase for hepatocellular carcinoma and extrahepatic cholangiocarcinoma. In women there was increased risk of extrahepatic cholangiocarcinoma and gallbladder cancer. Women with high BMI in early adulthood had increased risk of intrahepatic cholangiocarcinoma. Reduced cancer-specific survival was found for all hepatobiliary malignancies in women with overweight and obesity. In men, reduced survival was observed in individuals with obesity for all hepatobiliary cancers, except gallbladder cancer. Increased risk of cancer-death per 5 kg/m2 BMI increase was found for hepatocellular carcinoma, intra-, and extrahepatic cholangiocarcinoma in women. For men, 5 kg/m2 BMI increase was positively associated with cancer-death from intrahepatic cholangiocarcinoma. DISCUSSION: This study supports the notion of an increased risk of hepatobiliary cancers with increasing BMI, with sex and age variations. The findings also suggest a higher risk of cancer-death with increasing BMI.