CD56 expression aids in the differential diagnosis of cholangiocarcinomas and benign cholangiocellular lesions.

CD56 (neuronal cell adhesion molecule, N-CAM) has been reported in neuroendocrine tumours and as a marker of reactive biliary epithelial cells. However, up to date, it is not used to distinguish malignant from non-malignant biliary lesions. In this study, we systematically examined CD56 expression on 98 tumours arising from the biliary tree as well as intrahepatic conditions with reactive neoductules. When neuroendocrine carcinomas are excluded, only 4 of 32 (12.5%) cholangiocarcinomas expressed CD56, 2 of which showed clear cell morphology. Reactive bile ductules adjacent to cirrhotic nodules as well as in focal nodular hyperplasia were CD56 positive. Twelve of 17 (70.5%) bile duct adenomas were CD56 positive, whereas von Meyenburg complexes expressed CD56 only very focally in less than 5% of lesional cells. Bile duct cysts were negative for CD56 with the exception of focally interspersed neuroendocrine cells, similar to that seen in segmental bile ducts. Thus, if van Meyenburg complexes are excluded, CD56 can be used to differentiate intrahepatic non-neoplastic from neoplastic proliferations, which is a helpful diagnostic tool in small liver biopsies.