To investigate the structure and potential diagnostic utility of the detection of EWS-WT1 chimeric RNA in desmoplastic small round cell tumor, 12 examples of this entity and 49 other tumors that enter in its differential diagnosis were studied by reverse transcriptase polymerase chain reaction for the presence of EWS-WT1, EWS-FLI-1, PAX3-FKHR, and PAX7-FKHR chimeric transcripts.     ///    PAX3/PAX7-FKHR chimeras were present in 9 of 13 alveolar rhabdomyosarcomas but not in any other tumors. 