Descriptive epidemiology of biliary tract cancer incidence and geographic variation in Japan

ObjectiveThe epidemiologic features of each biliary tract cancer (BTC) subtype have not been studied and disclosed in detail. The objective of this study was to provide an up-to-date description of the epidemiologic features of BTC by subtypes, especially in terms of the geographic variation of its incidence. MethodsWe calculated the age-standardized incidence rate (ASR) of each BTC subtype at national and prefectural levels using the data from the national cancer registry in 2016 and 2017. The geographic distribution of each BTC subtype incidence was assessed by calculating the ASR ratio (ASRR) against median ASR at the prefectural level and reflecting them on the Japanese map. ResultsA total of 58 438 people diagnosed with malignant BTC were registered in the national cancer registry in 2016 and 2017 [12 497 for intrahepatic bile duct cancer (IHBDC), 16 568 for gallbladder cancer (GBC), 24 602 for extrahepatic bile duct cancer (EHBDC), 4613 for ampulla of Vater cancer (AVC) and 158 for others]. ASR was higher in men than in women for IHBDC, EHBDC and AVC, and similar between men and women for GBC. The ASR of EHBDC was approximately 2 times higher than those of the other subtypes for men and similar to that of GBC for women. The geographic distribution of ASRR was different among BTC subtypes, with larger variability in EHBDC, which was remarkably higher in the north-eastern region in both men and women. ConclusionThe pattern of the geographic distribution of incidence in each BTC subtype was different, which suggests different etiology among subtypes.