Desmoplastic small round-cell tumor of the paratesticular region: report of an adult case with demonstration of EWS and WT1 gene fusion using paraffin-embedded tissue.

Desmoplastic small round-cell tumor typically occurs in the abdomen of young men, but it can also develop at other anatomic sites and in older people, presenting greater diagnostic difficulties. We report a case of this tumor arising from the paratesticular region in a 43-year-old man. The tumor showed histologic, immunohistochemical, and ultrastructural evidence of multilineage differentiation, including epithelial, mesenchymal, and neuronal features. In addition, the presence of an EWS and WT1 chimeric messenger RNA was demonstrated by the reverse transcriptase-polymerase chain reaction using an EWS exon 7 primer and WT1 exon 8 and exon 9 primers, which revealed single polymerase chain reaction products with a junction of EWS exon 7 to WT1 exon 8. Our study demonstrates that desmoplastic small round-cell tumors of the paratesticular region share not only morphologic but also molecular genetic features with those of the abdomen and that reverse transcriptase-polymerase chain reaction analysis using paraffin sections is useful for a conclusive diagnosis.