Primary intrathoracic dermatofibrosarcoma protuberans.

Dermatofibrosarcoma protuberans (DFSP) is defined as a low-grade sarcoma derived from an uncertain cell of origin in the reticular dermis. We report a fibrosarcomatous variant of DFSP (FS-DFSP) that arose primarily in the deep thoracic soft tissue. The patient was a 9-year-old girl who presented with dyspnea and low-grade fevers without a clinically detectable mass or a history of skin lesion. Imaging studies revealed a 10-cm mass entirely confined within the thoracic cavity. Three years after a marginal excision with adjuvant chemotherapy and radiotherapy, the tumor recurred in the paraspinal region. Histologically, the primary and recurrent tumors comprised a high-grade spindle cell sarcoma, with a small component of storiform, low-grade, CD34-positive spindle cells, classic for an ordinary DFSP. The diagnosis of FS-DFSP was confirmed molecularly by the demonstration of a COL1A1-PDGFB fusion by fluorescence in situ hybridization and reverse transcription-polymerase chain reaction analyses. To our knowledge, this is the first documented case of a genetically confirmed deep-seated DFSP without an associated superficial soft tissue or dermal component. The implication of this case on expanding the clinical spectrum of DFSP will have to be elucidated in future studies by applying molecular pathologic tools in deep-seated sarcomas in the proper morphologic context.