Desmoplastic small round cell tumor: a clinicopathologic, immunohistochemical and molecular study of four patients

Desmoplastic small round cell tumor (DSRCT) is a rare but highly aggressive tumor that usually occurs in the abdominal cavity of young males. Immunohistochemical staining plays an important role in the differentiation of DSRCT from other small round cell neoplasms. Recently, a novel translocation of chromosome 11 and 22 [t(11;22)(p13+q12)] was identified in DSRCTs, which could result in the formation of the chimeric EWS-WT1 fusion gene. Reverse transcriptasepolymerase chain reaction (RT-PCR) has been applied to detect the fusion gene in fresh tissue and confirm the diagnosis. Only a few studies using RT-PCR with formalin-fixed and paraffin-embedded (FFPE) tissue sections to detect the specific transcript have been reported.

We collected four patients who had been diagnosed with DSRCT from the archives of the Department of Pathology, National Taiwan University Hospital, between 1996 and 2006. The clinical information and histologic sections of the patients were reviewed. Panel of primary antibodies including cytokeratin, vimentin, desmin and WT-1 were used for immunohistochemical staining. RNA extracted from the FFPE tissue sections was used for RT-PCR to identify the transcript of EWS-WT1.

All four patients were male, with a mean age of 24 years. All of the tumors originated in the abdominal cavity and liver metastases were found in two patients. Two patients died of disease within 2 years, and the other two remained alive with disease. Histologically, the tumors were composed of nests of primitive small round cells within a desmoplastic stroma. Immunohistochemically, all the tumor cells were reactive to cytokeratin, vimentin, desmin and WT-1. The characteristic EWS-WT1 fusion gene could be identified in the FFPE specimens of all three patients who had tissue sections available for RT-PCR analysis.

DSRCT is an aggressive tumor that usually occurs in the peritoneum of young males. The tumor is characterized by the expression of cytokeratin, vimentin, desmin and WT-1. RT-PCR, using paraffin-embedded tissue sections, can effectively detect the characteristic EWS-WT1 fusion gene transcript.