Enhancer of Zeste Homologue 2 (EZH2) expression in malignant and benign hepatic tumors K. Dezso * , V. Szabó, E. Bugyik, K. Schlachter, S. Paku, Z. Schaff, P. Nagy * Semmelweis University, 1st Dept. of Pathology, Budapest, Hungary Objective: The immunohistochemical demonstration of Enhancer of zeste homologue 2 (EZH2) proved to be a useful marker in several tumor types, including hepatocellular carcinomas.In order to recognize the diagnostic value of this protein in hepatic tumors we have investigated the presence of EZH2 in the most common liver neoplasms. Method: The presence of EZH2 has been studied by standard immunohistochemistry in several formalin-fixed paraffin-embedded tumor samples (hepatocellular adenoma, hepatocellular carcinoma, cholangiocarcinoma, hepatoblastoma, metastatic liver tumors and primitive childhood tumors). Results: Forty of 44 hepatocellular carcinomas, 22 of 23 cholangiocarcinomas, 29 of 31 hepatoblastomas and 14 of 17 metastatic liver tumors stained positively, but all the investigated hepatocellular adenomas (n = 24) and proliferating biliary structures were negative. The other primitive childhood tumors that were examined all expressed EZH2. Conclusion: Based on these results EZH2 is a sensitive marker of malignancy in hepatic tumors regardless of their histogenesis. In routine surgical pathology EZH2 could be helpful to diagnose hepatocellular carcinomas and it might be the first marker to distinguish transformed and reactive cholangiocytes.