The American journal of pathology
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Desmoplastic small round cell tumor is a recently described entity associated with fusion of the EWS and WT1 genes and with expression of a chimeric transcript. 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. Detection of chimeric transcripts by reverse transcriptase polymerase chain reaction is a very specific aid in differential diagnosis of developmental tumors and further establishes desmoplastic small round cell tumor as a distinct entity.