Comparison of Incidence of Intrahepatic and Extrahepatic Cholangiocarcinoma - Focus on East and South-eastern Asia

Background: The term "cholangiocarcinoma" was originally used only for intrahepatic bile duct (adeno) carcinomas, but is now regarded as inclusive of intrahepatic, perihilar, and distal extrahepatic tumors of the bile ducts. A rise in incidence of intrahepatic cholangiocarcinoma has been recently reported in Western countries but comparatively little is known about recent cholangiocarcinoma incidence trends in East and South-Eastern Asia. Methods: We compared age-adjusted incidence rates of both intrahepatic and extrahepatic cholangiocarcinomas, as well as coding practices, using data from 18 cancer registries in Asia and 4 selected registries in Western countries. Intrahepatic cholangiocarcinoma incidence rates were calculated after reallocation of cases with unknown or unspecified histology among liver cancer cases. Results: Age-adjusted incidence rates of intrahepatic cholangiocarcinoma varied by more than 60-fold by region. The highest rates were found in Khon Kaen, Thailand, where 90% of liver tumors were cholangiocarcinomas. The next highest rates were found in the People's Republic of China, followed by the Republic of Korea. The highest age-adjusted incidence rate for extrahepatic cholangiocarcinoma was found in Korea. Coding practices for perihilar (Klatskin tumor) or unspecified sites of cholangiocarcinoma differed from one cancer registry to the other. The proportion of Klatskin tumors among cholangiocarcinomas was less than the one reported in clinical settings. Conclusion: Developing a consistent and uniform topographical classification for acceptable coding practice to all health professionals is necessary. In addition, epidemiological research on risk factors according to anatomical location (intrahepatic versus extrahepatic) and the macroscopic appearance and/or new histological classification of cholangiocarcinoma is also needed.