Malignant melanoma showing ganglioneuroblastic differentiation: report of a unique case.

We report a case of metastatic malignant melanoma in an inguinal lymph node, expressing ganglioneuroblastic differentiation. This was characterized by the presence of discrete nests and islands of large ganglion cells with abundant cytoplasm and eccentric nuclei with prominent nucleoli admixed with smaller primitive neuroblasts. The cells were separated by pale pink fibrillar material representing neuritic cell processes. These foci of ganglioneuroblastoma were seen over a background of an otherwise typical metastatic epithelioid, focally melanotic, malignant melanoma. Immunohistochemistry showed positivity for neurofilament, synaptophysin, chromogranin, vasoactive intestinal peptide, and glial fibrillary acidic protein in the areas with ganglioneuroblastic differentiation, but not in the melanocytic component. Conversely, HMB45 positivity was expressed by the melanocytic cells only. S-100 protein and Melan-A, a putative melanocytic marker, showed positivity in both melanocytic and ganglioneuroblastic components. Ultrastructurally, neuritic cell processes and dense core neurosecretory granules were identified in the ganglionic and neuroblastic cells. A subsequent nodal metastasis in the same region showed focal neuroblastic differentiation without the ganglionic element. No evidence of neuronal or ganglionic differentiation was seen in the primary skin melanoma.