Intrahepatic cholangiocarcinoma with predominant ductal plate malformation pattern: an unusual mimicker of benign lesion

Case Report: Background Intrahepatic cholangiocarcinoma with predominant ductal plate malformation pattern is a recently discovered rare entity. This lesion has similar histological features seen in a ductal plate malformation, which resembling ductular reaction and would be developped from hepatic progenitor cells. Materials, methods and results A 57-year-old woman presented a liver mass in the right lobe. A diagnosis of biliary adenofibroma was suggested on the first biopsy. In a second stage, a right hepatectomy was performed. On gross examination, we found a lesion 5,5 cm long, whitish, firm, well-demarcated, homogeneous, located within segment 7. On histology, this lesion was unencapsulated and pushing out the rest of the non-tumorous liver parenchyma. The tumour is characterised by a scattered well- differentiated ductular proliferation within a dense fibrous stroma. Glandular structures with irregular dilated lumens are lined by a low-colmunar-to-cuboidal cells with high nucleocytoplasmic ratios and round vesicular nuclei. There was no marked pleomorphism. Usually, no mucin is visualised. Some immunohistochemistry was realised, Arginase 1, Hep-Par1 and S100 were negative. All tubules expressed CK7 and CK19 heterogeneously. EMA demonstrated an apical diffuse marking on tumor cells. EPCAM revealed an extended basolateral positivity and NCAM, a partial basolateral positivity. Immunohistochemistry for P53 was wild-type. The proliferation index assessed by ki67 was low, around 5%. Finally, a diagnosis of intrahepatic cholangiocarcinoma with predominant ductal plate malformation pattern was retained. Conclusion Intrahepatic cholangiocarcinoma with predominant ductal plate malformation pattern is an unusual entity that can mimic a benign lesion.