Melanotic neuroectodermal tumour as a predominant component of an immature testicular teratoma

A case of melanotic neuroectodermal tumour (MNT), or so-called retinal anlage tumour, as a predominant component of an immature testicular teratoma is presented. The patient was a 17-year-old man who furthermore had a mature mediastinal teratoma. The MNT was composed mainly of two cell types: small immature neuroblast-like cells and large columnar or cuboidal epithelial-like cells with or without melanin granules. The tumour cells were arranged in solid formations, nests, cords, alveolar and pseudoglandular structures with cleft-like or glomeruloid-like spaces. Myogenic differentiation was found in minor foci. Immunohistochemistry showed both neuroepithelial and mesenchymal features with positive staining reaction for neuron-specific enolase (NSE), S-100 protein (S-100), melanoma antigen (HMB45), cytokeratin and vimentin. Vimentin, desmin and actin were present in the myoid cells. To the best of our knowledge this is the first reported case of MNT originating in the testis. As this tumour component occurred in an immature teratoma, neuroectodermal differentiation of germ cell origin is considered most likely.