Answer: Dermatofibrosarcoma protuberans

Histology: This tumor is centered in the deep dermis and subcutaneous tissue. It shows a storiform pattern, with tumor cells radiating around a central point producing spokes grouped at right angles to each other. The periphery of the tumor shows entrapped fat cells. Giant cells, xanthoma cells, or inflammatory cells are absent. Immunostains for CD34 were uniformly positive in the tumor cells. The tumor cells were negative for HMB45, CD68, Melan-A, and S-100, and factor 13a.

Discussion: Dermatofibroma (benign fibrous histiocytoma of the skin) is a dermal tumor that is more heterogeneous in its cellular composition, containing fibroblasts, myofibroblasts, histiocytes, xanthoma cells and occasional multinucleate giant cells. Dermatofibroma typically labels for Factor 13a, but not for CD34. The absence of S-100 protein reactivity in DFSP would help to distinguish it from a diffuse neurofibroma or from the desmoplastic variants of melanoma. Fibromatoses should have a hypocellular, fascicular growth pattern, without the storiform pattern of DFSP. Deep fibromatoses should demonstrate nuclear labeling for ß-catenin. Dermatofibrosarcoma protuberans (DFSP) is considered a fibrohistiocytic tumor of intermediate malignancy.

Dermatofibrosarcoma typically presents in early or middle adult life. Males appear to be more frequently affected than females. Lesions are seen most frequently on the trunk and proximal extremities followed by the head and neck. DFSP has a significant (50%) recurrence rate, and therefore must be treated by wide local excision (2-3cm margins). Regional or distant metastasis is rare.