Neurosarcomatous transformation in malignant melanoma: an ultrastructural study.

Six cases of desmoplastic melanoma were studied by light and electron microscopy. The tumors fulfilled one or more of the following criteria: (1) having the presence of atypical intraepidermal melanocytic proliferation bordering the primary lesions; (2) an antecedent history of melanoma at the site of recurrence; (3) a metastatic lesion in the direct lymphatic drainage route of a previously excised melanoma. Premelanosomes were not identified in the neoplastic cells. Ultrastructural features common to the six tumors were interpreted as evidence of Schwann cell differentiation, i.e., neurosarcomatous transformation occurring in malignant melanoma. The ultrastructural findings provide further support for the concept that melanocytic lesions may simulate tumors of Schwann cell origin, presumably reflecting the common embryologic origin of the two cell types from the neural crest.