Hepatoblastomas in the mummichog, Fundulus heteroclitus (L.), from a creosote-contaminated environment: a histologic, ultrastructural and immunohistochemical study

A detailed histologic, immunohistochemical and ultrastructural description of two cases of hepatoblastoma, a primitive liver cell neoplasm, is provided from mummichog, Fundulus heteroclitus (L.), inhabiting a creosote-contaminated environment in the Elizabeth River, Virginia, USA. Both neoplasms were multifocal and comprised of undifferentiated embryonal cells with a high nuclear to cytoplasmic ratio. One case was characterized by a prominent macrotrabecular arrangement of tumour cells, whereas the other was solid in organization and undifferentiated. Tumour cells in some areas formed rosettes or pseudorosettes characteristic for hepatoblastoma. Focal areas within the macrotrabecular tumour were poorly differentiated, exhibiting a solid cellular arrangement. Strong immunolabelling with antibody C-219 indicated elevation and altered patterns of P-glycoprotein expression in both cases. In case 1, plasma membranes and tumour cell cytoplasm, but not bile canaliculi, were strongly labelled. However, in case 2, the macrotrabecular lesion, bile canaliculi were prominently labelled by the C-219 antibody with only patchy immunolabelling of tumour cell cytoplasm. Ultrastructurally, neoplasms from both specimens were composed of small, closely apposed, undifferentiated embryonal cells with scant cytoplasm resembling developing hepatocytes. The macrotrabecular lesion (case 2) exhibited a prominent tubular organization with well-developed bile canaliculi and constituent cells with abundant organelles. Based on histologic pattern, immunohistochemistry and ultrastructural features, these undifferentiated liver lesions are distinct from hepatocellular carcinoma reported in this species and warrant a diagnosis of hepatoblastoma.