Signet-ring cell melanoma: a potential diagnostic pitfall.

[liposarcoma]

: 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 S 100 , 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 .