OBJECTIVETo study the clinicopathologic features of combined hepatocellular-cholangiocarcinoma (cholangiolocellular type, CLC type) with stem cell features and its relationship to hepatic progenitor cells (HPCs).

METHODSClinical and histologic features of 26 cases of combined hepatocellular-cholangiocarcinoma (CLC type) were reviewed. Histochemistry was performed to confirm the type of mucin and immunohistochemical study was carried out for hepatocytic markers (Hep Par-1 and AFP) and biliary/HPCs markers (CK7, CK9, EMA, EpCAM, NCAM, CKIT).

RESULTSThe age of patients ranged from 51 to 82 years (mean 64 years). All 26 cases contained CLC and hepatocellular carcinoma components. CLC area was composed of mixtures of small monotonous glands with abundant fibrous stroma and lymphocytic infiltrate. Tumor cells were cuboidal, smaller in size than normal hepatocytes, with basophilic cytoplasm and round nuclei. All cases, especially at the tumor boundary, showed HCC-like trabecular areas characterized by mildly atypical tumor cells with abundant eosinophilic cytoplasm and little stroma. Out of 26 cases, 21 showed definite glandular formation with mucin production, representing intrahepatic cholangiocarcinoma areas. The three distinct areas showed transitional zones merging with each other. The surrounding liver tissue showed cirrhosis and chronic hepatitis with varying degrees of fibrosis and periportal ductular reaction. Immunohistochemistry showed that biliary/HPC markers (CK7, CK9, EMA, EpCAM, NCAM and CKIT) were strongly positive in CLC area in almost all cases, similar to the staining pattern of ductular reaction. In HCC-like areas, CK7 and CK19 were positive in all cases and the expression rates of EMA, EpCAM, NCAM, CKIT, AFP, Hep Par-1 were 80.8% (21/26), 88.5% (23/26), 84.6% (22/26), 88.5% (23/26), 46.2% (12/26) and 53.8% (14/26) respectively, similar to the staining pattern of intermediate hepatocytes. In ICC areas, CK7, CK9, EMA and EpCAM were positive in all cases without the expression of NCAM and CKIT.

CONCLUSIONThe clinicopathologic findings and immunohistochemical results in this study highly suggest a hepatic progenitor cell origin of combined hepatocellular-cholangiocarcinoma (CLC type).