Desmoplastic malignant melanoma: A light and electron microscopic study of two cases.

This light and electron microscopic study of two recent cases of desmoplastic malignant melanoma (DMM) attempts to resolve the conflict in views regarding the nature of the cells responsible for the desmoplasia associated with this clinicopathologic entity. On the basis of evidence presented, it is concluded that the cells are dedifferentiated tumor cells with fibroblastic features and probably functions, rather than host engendered fibroblasts in response to invasive melanoma. The evidence includes: observation of macular desmosomes between tumor cells, an unheralded feature previously noted in amelanotic and melanotic melanomas; electron microscopic observation of fibroblast-like cells by others in spindle cell squamous carcinomas; and light microscopic features of malignancy including vascular invasion in one of the two cases. A reproducible light microscopic pattern diagnosis of this variant of malignant melanoma is reaffirmed in both cases.