Tumors of the liver, intrahepatic and extrahepatic bile ducts as well as the gallbladder are very heterogeneous and show different biological behavior. The 4‑stage (i.e. well, moderately, poorly and undifferentiated) grading system for hepatocellular carcinoma proposed by the WHO takes tumor size and architecture as well as the extent of cell and nuclear pleomorphism into account. In addition, the WHO defines some special forms of hepatocellular carcinoma. For carcinomas of intrahepatic bile ducts the WHO provides a 3‑stage (well, moderately and poorly differentiated) grading system, which is based on architectural and cytological changes. At this localization there are also additional special histological forms that have to be dealt with outside the grading system described. The WHO proposes a 3‑stage (well, moderately and poorly differentiated) grading system for carcinomas of the extrahepatic bile ducts and the gallbladder, which considers the proportion of glands contained within the adenocarcinoma. Similar to cancers of the liver and intrahepatic bile ducts there are also numerous special histological forms, which are explained in this article.
Keywords: Hepatocellular carcinoma; Intrahepatic cholangiocarcinoma; Special histological forms; Tumor heterogeneity; WHO grading system.