title: Signet-ring cell melanoma: a potential diagnostic pitfall.
abstract: Malignant melanoma is commonly known as the great mimicker and can present in various clinical manifestations and with diverse morphological variants. One of the rare histological variants is the signet-ring cell type. The signet-ring morphology has been reported in numerous other neoplasms including adenocarcinoma, lymphoma, liposarcoma, squamous cell carcinoma, and basal cell carcinoma. We report a rare case of primary signet-ring cell malignant melanoma in a 62-year-old man. He initially presented with an enlarging nevus on his right flank with surrounding erythema. A biopsy showed atypical epithelioid and signet cells with prominent nucleoli and occasional mitoses. Initial diagnosis favored metastatic signet-cell carcinoma of gastrointestinal origin. Review of the biopsy and immunohistochemical analysis revealed the malignant signet-ring cells stained with S100, vimentin, and melanoma cocktail, in keeping with melanoma. The signet-cell morphology can be found in a variety of other malignancies. To prevent potential misdiagnoses, thorough histological examination should be aided by an appropriate immunohistochemical panel to confirm melanoma and exclude erroneous differentials.
authors.affiliation: Department of Pathology and Molecular Medicine, McMaster University, St Joseph's Hospital, Hamilton, Ontario.
authors.forename: Linda
authors.initials: L
authors.lastname: Kocovski
authors.forename: Salem
authors.initials: S
authors.lastname: Alowami
mesh_terms: D018279:Carcinoma, Signet Ring Cell / Q000473:pathology* / Q000556:secondary; D003937:Diagnosis, Differential; D006801:Humans; D008297:Male; D008545:Melanoma / Q000737:chemistry* / Q000473:pathology* / Q000601:surgery; D008875:Middle Aged; D009418:S100 Proteins / Q000032:analysis; D012878:Skin Neoplasms / Q000737:chemistry* / Q000473:pathology* / Q000601:surgery; D014746:Vimentin / Q000032:analysis
chemical_list: D009418:S100 Proteins; D014746:Vimentin