Superficial CD34-positive Fibroblastic Tumor
This distinctive low-grade neoplasm of the skin and subcutis is rare, with few reported cases.
Most have occurred in middle-aged adults, with a slight male predominance, and a predilection for the lower extremities, followed by upper extremities, buttock, and shoulder.
Histology demonstrates highly cellular fascicles and sheets of spindled to epithelioid cells with abundant eosinophilic, often glassy cytoplasm and moderate-to-marked pleomorphism (Fig. 5).
There is morphologic overlap reported with PRDM10-rearranged soft tissue tumors.
By IHC, there is strong CD34 expression (Fig. 5B), and keratins are positive in 70% of cases. The prognosis in reported cases has been excellent.
FIGURE 5. Superficial CD34-positive fibroblastic tumor. A, The tumor is composed of sheets of variably pleomorphic and epithelioid cells with abundant, glassy eosinophilic cytoplasm. Mitotic activity is minimal, in contrast to undifferentiated pleomorphic sarcoma. B, IHC for CD34 is diffusely positive. Keratins are also often positive (not shown).