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Case Reports

Abstract

Malignant melanoma (MM) is commonly recognized histopathologically by identification of atypical epithelioid cells with abundant cytoplasm and melanin pigment. Amelanotic melanoma may require immunohistochemistry to confirm its melanocytic origin. Rare variants of melanoma have morphologic and immunophenotypic presentations that mimic neoplasms of other cell origins. Such histopathologic variants include desmoplastic, clear (balloon) cell, signet ring, plasmacytoid, rhabdoid, myxoid, and small cell variants. We encountered a rare presentation of MM in which the tumor cells contained abundant lipidized changes. An 80-year-old female, on routine skin check, was found to have a pink papule with speckled brown dots of unknown duration on the right upper back. Shave biopsy revealed a predominantly dermal tumor of atypical cells with abundant pink to foamy cytoplasm abutting an effaced epidermis with lichenoid regression. There was a brisk lymphocytic host response. The tumor cells were positive for adipophilin (negative for androgen receptor), SOX10, and MART1, with focal HMB45 expression, consistent with MM, 1.4 mm, 1 mitosis/mm^2. No ulceration, lymphovascular/neural invasion, or satellitosis were detected. Lipidized cells can be seen in entities such as dermatofibroma and in clear cell MM by electron microscopy, but foamy cells in MM are highly unusual. Adipophilin, a lipid droplet-associated protein, is expressed in a subset of malignant melanomas and has been associated with advanced pathological stage and poorer clinical prognosis, making it a potential prognostic marker in tumors with a lipogenic phenotype. This case contributes to the list of MM histopathologic variants, with potential to serve as a prognostic marker.