Epithelial and mixed hepatoblastoma in the adult. Histological observations and general considerations.

Two instances of hepatoblastoma in adults are reported, with one case representing a purely epithelial, the other a mixed epithelio-mesenchymal variant. The purely epithelial tumour, consisting entirely of so-called fetal elements, was present in the liver of a 35-year-old woman without any other hepatic changes, whereas the mixed tumour developed in the coarsely nodular liver of a 73-year-old man with a currently inactive cirrhosis. Besides the epithelial component, this case held predominantly indifferent spindle-shaped and histiocytic mesenchymal cells which frequently gave rise to osteoid and to bony trabeculae, and on occasion also to vascular structures, biliary ducts and even to groups of hepatocytes. The cytological and histological picture of both cases is comparable even in its details to that seen in the hepatoblastomas of early childhood. This concordance should be insisted upon as a diagnostic pre-condition if a mixed tumour in the adult, consisting of several components, is to be accepted as a hepatoblastoma. This similarity also enables us to recognize the purely epithelial variant of the hepatoblastoma in the older patient as belonging to this tumour category, and to separate it from other hepatic carcinomas. It is suggested that in these tumours the pluripotent cells, or the cells that have again become pluripotent, are derived from differentiated hepatocytes; no evidence in favour of the existence of a particular cellular subpopulation or of "stem cells" has been found.