Melanoma associated with a dysplastic nevus: report of two cases with unusual sebocyte-like melanocytes in the nevus part of the lesion.

We present two cases of melanoma arising in a dysplastic nevus that contained intradermal sebocyte-like melanocytes characterized by a scalloped dark-staining nucleus surrounded by the pale multivacuolated cytoplasm imitating sebaceous differentiation. Both patients were women, aged 49 and 55 years. Location included the back and temporal area. Microscopically, both cases had the following features in common: the melanoma in situ, which was of the superficially spreading type, was associated with a dysplastic compound nevus, in which the sebocyte-like cells were identified in the intradermal nevus part of the lesion. The sebocyte-like cells comprised a minor component but were immediately recognizable and appeared as cells with multivacuolated neoplasm and scalloped nuclei arranged in nests. Some contained melanin in the cytoplasm. They stained positively for S-100 protein and melan A but were EMA and HMB-45 negative. The conventional part of the nevi demonstrated the same phenotype, with the exception of the melanocytic nests located at the dermoepidermal junction that were HMB-45 positive. The cases are discussed in the context of the pertinent literature.