SIGNET-RING CELL MELANOMA MIMICKING ADENOCARCINOMA - A CASE-REPORT

The fine needle aspiration findings in a lymph node involved by signet -ring cell melanoma, a very rare variant of malignant melanoma, are re ported. 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 ab undant, eosinophilic cytoplasm; many of them exhibited a signet-ring a ppearance. Melanin pigments were identified in a small proportion of t umor cells, and a diagnosis of metastatic melanoma was made. The subse quent lymph node excision revealed a metastatic tumor composed of poly gonal and signet-ring cells that were positive for S-100 protein and H MB-45 but not cytokeratin. Nearly all reported cases of signet-ring ce ll melanoma occurred as metastatic or recurrent disease. It is importa nt not to mistake signet-ring cell melanoma for adenocarcinoma in aspi ration cytology, and a constellation of clinical features and of histo chemical and immunohistochemical findings enables a correct diagnosis to be reached.