Sebocyte-like cell primary cutaneous melanoma: a rare cytologic variant of malignant melanoma.

Although rising incidence rates of cutaneous melanoma have been observed during the last 4 decades in white populations worldwide, the sebocyte-like cell variant has been described only twice in the literature to date. In our case, a 64-year-old man presented for evaluation of a changing pigmented lesion on the left upper back. Excision of the lesion revealed an invasive melanoma with a Breslow depth of 3.3 mm. Microscopic sections showed a predominantly dermal-based tumor composed of sheets and nests of enlarged epithelioid melanocytes, most of which showed an uncommon phenotype with multivacuolated cytoplasms and scalloped nuclei, features that gave them a strong resemblance to mature sebocytes. The lesional cells expressed S100 protein, Melan-A, and p16, whereas adipophilin was positive only within the sebocyte-like component of the neoplasm and showed focal nonspecific staining. The patient's sentinel lymph node biopsy was positive for micrometastases, although a subsequent position emission tomography scan was unremarkable. Sebocyte-like melanocytes are a rare distinctive type of melanocytes that can be found mostly in benign but also in malignant melanocytic lesions. They usually present focally within the lesions and, therefore, do not represent a diagnostic problem in nevus or primary cutaneous melanoma. However, when sebocyte-like melanocytes are the main cellular component of a melanocytic lesion or when they are found in the context of metastatic melanoma, they may create a potential diagnostic pitfall; for this reason, awareness of this cell type is important.