Myoid differentiation and EMA expression in fibrosarcomatous dermatofibrosarcoma protuberans.

Dermatofibrosarcoma protuberans (DFSP) is a relatively unusual, locally aggressive cutaneous tumor of intermediate malignancy. Fibrosarcomatous DFSP (FS-DFSP), a rare variant of DFSP, has a higher tendency for recurrence and metastasis. Recently, a small number of cases of another variant of FSDFSB characterized by areas of myoid differentiation have been reported. We present here a 35 yearold female patient with myoid differentiation in FS-DFSP. The tumor on the left scapular region had slowly grown over six years. Examination revealed a domeshaped, firm, nontender, violaceous dermal nodule. Histologically, it was composed of a monotonous spindle cell population arranged predominantly in a storiform pattern and to a lesser extent in a fascicular fibrosarcomatous pattern with a parallel arrangement of the cells. Immunohistochemically, the tumor cells showed diffuse expression for vimentin and CD34. In the center of the tumor areas with frequent mitosis, hypercellular and negative reactive for CD34 were seen. In addition, approximately 10% of the cells were positive for epithelial membrane antigen. Myoid differentiation was found around the blood vessels. The myoid areas were positive for smooth muscle actin and negative for desmin. It is possible that the presence of hyperplastic myofibroblasts is a reactive phenomenon to the proliferation of tumor cells. We believe that this finding around blood vessels may be present in DFSP or FS-DFSP. However, when myoid areas, myoid fascicles and myoid nodules are seen in the stroma, it may be a new morphological variant of DFSP and/or FS-DFSP.