Primary desmoplastic small cell tumor of soft tissues and bone of the hand

Desmoplastic small cell tumor (DSCT) is a high-grade malignant neoplasm tha t shows polyphenotypic differentiation. its almost exclusive involvement of serosal surfaces (particularly peritoneum) has led to the consideration of a putative "mesothelioblast" as the cell of origin. Although an extraseros al case involving the brain (presumably arising from the dura) has been rep orted, to date no case primary in the bone or soft tissues has been documen ted. The authors describe a 34-year-old man who presented with a 3-year his tory of pain in the right hand and a recently noted mass in the hypothenar area. Open biopsy followed by wide en bloc excision in combination with ind ex ray resection was performed. Subsequently, the patient underwent ipsilat eral axillary lymph node dissection. Extensive radiologic workup at the tim e of presentation and 12 months later revealed no tumor in the chess or abd omen. The patient was treated with an HD-CAV chemotherapy regimen(cyclophos phamide, doxorubicin, vincristine;, ifosfamide, etoposide) and was free of tumor until Is months later, at which time he developed multiple metastases in the lungs. Currently, he is alive with tumor and in poor condition. The histologic sections of the mass displayed the characteristic features of D SCT involving bone and soft tissue. Immunohistochemical stains showed posit ivity of the tumor cells for muscle marker (desmin), neuroendocrine markers (chromogranin, synaptophysin), and epithelial markers (keratins CAM5.2, AE 1:AE3, epithelial membrane antigen). Chimeric transcripts were detected by reverse transcriptase-polymerase chain reaction, indicating the presence of EWS-WT1 gene fusion, which is characteristically associated with DSCT. Seq uence analysis showed in-frame fusion of EWS exon 9 to WT1 exon 8-a variant not documented in any other case. This is a unique example of DSCT primary in bone and soft tissues, which raises interesting questions about the his togenesis of this tumor type and its relationship to other small round cell tumors. Although the "mesothelioblast" hypothesis as the origin of DSCTs i s attractive, it does not account for the tumors that are located in the br ain or, as in this patient, in the soft tissues and bone. In addition, this patient demonstrates a rare variant of EWS-WT1 gene fusion not described i n DSCT involving serosal surfaces.