Melanin-containing hepatoblastoma with endocrine differentiation. An immunohistochemical and ultrastructural study

The authors previously have reported that hepatoblastomas may exhibit endocrine differentiation. This report describes a hepatoblastoma in which a melanocytic component was present in addition to endocrine differentiation.

The tumor, which arose in a 15-month-old girl, was subjected to conventional histologic, histochemical, immunohistochemical, and electron microscopic investigation.

The tumor had fetal and embryonal epithelial areas and osteoid. The presence of melanin could be suspected, even on the basis of gross examination. The melanin was found predominantly in macrophages but also was present in a few epithelial tumor cells. The tumor also had HMB45-immunoreactive melanocytic cells, and correspondingly, cells containing dopa-oxidase, an enzyme essential for melanin synthesis. Staining for chromogranin A and serotonin was seen in fetal-type cells, embryonal-type cells, and in epithelial cells of reactive bile ductules at the periphery of the tumor.

Primary melanin-containing tumors of the liver are extremely rare; only one such tumor, referred to as a "teratoid hepatoblastoma," previously has been described in detail. The combination of endocrine and melanocytic differentiation has not been reported previously in liver tumors but occurs in endocrine tumors of other organs. Although it is not possible to define exactly the histogenesis of the melanocytic cells in this tumor, it is most likely that these cells and the other components of the tumor derive from a pluripotent entodermal stem cell by multidirectional differentiation.