Abstract

Superficial CD34-positive fibroblastic tumors are recently described and uncommon tumors that can mimic dermatofibrosarcoma protuberans (DFSP) both clinically and histologically. Superficial CD34-positive fibroblastic tumors are low-grade fibroblastic tumors of the skin and subcutis. They typically present as a <5 cm slow-growing mass in the extremities of middle-aged adults. Here we report a unique case of a 28-year-old man with a superficial CD34-positive fibroblastic tumor mimicking a DFSP. The patient presented with a two month history of a 0.5 cm lump on his left upper arm. A punch biopsy revealed a deep dermal proliferation of atypical spindle cells that strongly expressed CD34 by immunohistochemistry. The deep aspect of the neoplasm showed a predominantly well-defined border. Given the deep dermal location and overall morphology, along with the strong CD34 expression, the tumor was originally diagnosed as a DFSP. However, additional workup showed the tumor cells to be immunoreactive to pancytokeratin and failed to show a PDGFRB gene rearrangement as seen in DFSP. Both entities may demonstrate morphologic and immunohistochemical overlap, but CD34-positive fibroblastic tumors are more cytologically pleomorphic with abundant glassy cytoplasm, nuclear enlargement with prominent nucleoli and are often immunoreactive for keratins. The boundaries of the tumor are more well-defined unlike the honeycomb infiltration seen in DFSP. The co-expression of CD34 and pancytokeratin, along with the nuclear pleomorphism and lack of PDGFRB gene rearrangement, led to a final diagnosis of superficial CD34-positive fibroblastic tumor. It is important to distinguish superficial CD34-positive fibroblastic tumor from DFSP, because the latter requires more aggressive follow-up as they tend to recur and have the potential for fibrosarcomatous transformation.

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