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 youn g 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 sho wed histologic, immunohistochemical, and ultrastructural evidence of multil ineage differentiation, including epithelial, mesenchymal, and neuronal fea tures. In addition, the presence of an EWS and WT1 chimeric messenger RNA w as demonstrated by the reverse transcriptase-polymerase chain reaction usin g an EWS exon 7 primer and WT1 exon 8 and exon 9 primers, which revealed si ngle polymerase chain reaction products with a junction of EWS exon 7 to WT 1 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-p olymerase chain reaction analysis using paraffin sections is useful for a c onclusive diagnosis.