Primary invasive signet-ring cell melanoma

The histopathological variants of malignant melanoma include the common typ e (lentigo maligna, superficial spreading melanoma, nodular melanoma, acrol entiginous melanoma), spindle cell, desmoplastic, balloon cell, pleomorphic (fibrohistiocytic), myxoid, small cell melanoma and malignant blue nevus. Recently, signet-ring cell melanoma was introduced as an additional cytolog ic variant. We describe a 72-year-old patient with a primary signet-ring ce ll melanoma of the skin located on the upper arm. Histopathologic examinati on disclosed a melanocytic tumor extending from the epidermis to the deep r eticular dermis. Numerous pleomorphic tumor cells showed large, intracellul ar vacuoles and oval to spindle-shaped nuclei at their periphery. Mitotic f igures and multinucleated melanocytes were also observed. Some of the signe t-ring cells exhibited cytoplasmatic periodic acid-Schiff (PAS)-positivity. Immunohistochemistry showed positive reaction of the tumor cells for S-100 , HMB-45 protein and vimentin, confirming their melanocytic differentiation . Tumor cells were negative for cytokeratins, epithelial membrane antigen ( EMA), and carcinoembryonic antigen (CEA). The signet-ring cell melanoma dis closed an invasion to Clark Level IV and tumor thickness of 2.2 mm. Signet- ring cell melanoma is a rare morphologic variant of melanoma. Its recogniti on is important for differentiation from other tumors featuring signet ring cells.