title: Signet-ring cell melanoma mimicking adenocarcinoma. A case report.
abstract: The fine needle aspiration findings in a lymph node involved by signet-ring cell melanoma, a very rare variant of malignant melanoma, are reported. The patient had a history of superficial spreading melanoma of the right foot, treated 10 years earlier by below-the-knee amputation. He presented with a right groin mass. Fine needle aspiration of the mass yielded poorly cohesive, large cells with eccentric nuclei and abundant, eosinophilic cytoplasm; many of them exhibited a signet-ring appearance. Melanin pigments were identified in a small proportion of tumor cells, and a diagnosis of metastatic melanoma was made. The subsequent lymph node excision revealed a metastatic tumor composed of polygonal and signet-ring cells that were positive for S-100 protein and HMB-45 but not cytokeratin. Nearly all reported cases of signet-ring cell melanoma occurred as metastatic or recurrent disease. It is important not to mistake signet-ring cell melanoma for adenocarcinoma in aspiration cytology, and a constellation of clinical features and of histochemical and immunohistochemical findings enables a correct diagnosis to be reached.
authors.affiliation: Institute of Pathology, Queen Elizabeth Hospital, Kowloon, Hong Kong.
authors.forename: W Y
authors.initials: WY
authors.lastname: Tsang
authors.forename: J K
authors.initials: JK
authors.lastname: Chan
authors.forename: L T
authors.initials: LT
authors.lastname: Chow
mesh_terms: D000230:Adenocarcinoma / Q000473:pathology*; D000368:Aged; D000369:Aged, 80 and over; D001707:Biopsy, Needle; D003937:Diagnosis, Differential; D006801:Humans; D007124:Immunoenzyme Techniques; D008207:Lymphatic Metastasis / Q000473:pathology* / Q000648:ultrastructure; D008297:Male; D008545:Melanoma / Q000473:pathology* / Q000648:ultrastructure