Paraganglioma-like dermal melanocytic tumor - A unique entity distinct from cellular blue nevus, clear cell sarcoma, and cutaneous melanoma

We are reporting a previously undescribed primary dermal melanocytic tumor identified by reviewing all dermal melanocytic tumors referred in consultation that did not qualify histologically as a previously described entity. From these cases, 8 were remarkably similar. We termed them "paraganglioma-like dermal melanocytic tumor" (PDMT) based on their nested growth pattern. This term is used descriptively and does not imply any histogenetic or biologic similarity to true paraganglioma. PDMT is primarily a tumor of the extremities of adult females (18-53 years, mean 35 years; males 2; females 6) which present as a dermal nodule (range, 0.5-4.2 cm; mean, 1.4 cm) composed of nests of clear to amphophilic oval cells separated by delicate fibrous strands. Nuclear atypia was mild and mitotic activity low (1-4 mitoses/10 HPF). Melanin was not obvious on light microscopy. Tumors expressed S-100 protein (8 of 8), MelanA (4 of 8), HMB-45 (8 of 8), and microphthalmia transcription factor (8 of 8) and lacked pancytokeratin (8 of 8) and smooth muscle actin (8 of 8). FISH analysis of 5 cases revealed an intact EWS gene locus, supporting absence of the clear cell sarcoma 12;22 translocation. Follow-up information in 8 patients (range, 35-92 months; mean, 54 months) indicated that all were alive without disease. PDMT comprises a clinically and pathologically unique subtype of dermal melanocytic tumors. Our study suggests a benign course, although a lesion of low malignant potential cannot be excluded.