Immunohistochemical expression of WT1 by desmoplastic small round cell tumor - A comparative study with other small round cell tumors

Desmoplastic small round cell tumors (DSRCTs) present a reciprocal chromoso mal translocation, t(11;22)(p13;q12), that results in fusion of Ewing's sar coma and Wilms' tumor (WT1) genes. The authors evaluated 15 DSRCTs and 71 o ther tumors often considered in the differential diagnosis for immunoreacti vity using a polyclonal antibody directed against the WT1 part of the chime ric protein resulting from this translocation. WT1 immunostaining was perfo rmed on paraffin material using the WT(C-19) antibody after heat-antigen re trieval. All the DSRCTs (15 of 15, 100%) demonstrated strong WT1 nuclear im munoreactivity. Ten of 14 nephroblastomas (71%) disclosed WT1-positive nucl ei in accordance with the staining reported by others, and rare and focal n uclear positivity was detected in two of 17 rhabdomyosarcomas. WT1 immunore activity was not observed in Ewing's sarcoma/primitive neuroectodermal tumo rs (zero of 21, 0%), neuroblastomas (zero of 17, 0%), or rhabdoid tumors of the kidney (zero of two, 0%). In nephroblastoma, differential diagnosis wi th DSRCT was not difficult: Clinical and morphologic data are not similar f or these two entities. The current study validates WT1 immunoreactivity as a useful marker to separate DSRCT from other small round cell tumors.