Metastatic dermatofibrosarcoma protuberans with fibrosarcomatous change in the absence of local recurrence. A case report of simultaneous occurrence with a malignant giant cell tumor of soft parts.

An unusual case of a metastasizing dermatofibrosarcoma protuberans with fibrosarcomatous change (DFSP-FS) is reported. The tumor metastasized to unusual sites, including soft tissues of the cheek, forearm, and retroperitoneum 5 years after surgical resection without local recurrence. In addition, the patient had a second, histologically distinct fibrohistiocytic tumor: a malignant giant cell tumor of soft parts. The occurrence of these two tumor types in the same patient highlights the relationship of DFSP to the family of fibrohistiocytic tumors. The late onset of metastases in the absence of local relapse, although a rare event, reflects the potential difficulty in predicting its biologic behavior. DFSP-FS may be a more aggressive tumor than ordinary DFSP.