Desmoplastic malignant melanoma: a study by conventional and electron microscopy.

A 61-year-old white man presented himself with a mass that had recurred on the chin. Conventional microscopy of sections from this mass showed atypical spindle cells surrounded by abundant collagen and resembled fibrosarcoma. Stains for melanin revealed pigment in the cytoplasms of the atypical spindle cells. Study of sections by electron microscopy demonstrated round, oval, and spindle-shaped cells having desmosomes and containing abundant melanosomes in varying stages of maturation. On the basis of both conventional microscopy and electron microscopy, the diagnosis was desmoplastic malignant melanoma. An unusual finding by electron microscopy was the presence of tubuloreticular intracytoplasmic inclusions in the neoplastic melanocytes.