Reverse-transcriptase polymerase chain reaction (RT-PCR) analysis, however, identified EWSR1-FLI1 fusion transcripts in both tumors, and the gene fusions were corroborated by FISH analysis with "in house" probes and confirmed by sequencing RT-PCR products.     ///    Cryptic EWSR1-FLI1 fusions in Ewing sarcoma: potential pitfalls in the diagnostic use of fluorescence in situ hybridization probes..     ///    "The occurrence of cryptic EWSR1-FLI1 fusions mandates that RT-PCR should be performed, particularly in those cases in which the genetic findings are not in agreement with the histologic picture.. "