Ewing sarcoma–peripheral neuroectodermal tumor of the kidney with a FUS–ERG fusion transcript

The Ewing family of tumors (EFTs) represents a neoplastic entity characterized by specific chromosomal rearrangements. The most commonly detected translocation involves fusion of EWSR1 to one of the genes encoding ETS family of transcription factors, usually FLI1 or ERG. In rare cases, FUS or FEV has been shown to substitute for EWSR1. The detection of specific translocations by fluorescence in situ hybridization (FISH), reverse transcription-polymerase chain reaction (RT-PCR), or both has become a diagnostic hallmark for the EFTs. We report here a case of small round blue cell tumor detected in the kidney of a 3-year-old girl. The use of FISH in combination with RT-PCR led to identification of a novel FUS–ERG fusion transcript in the tumor, with FUS exons 1–5 fused in-frame to ERG exons 6–9. The results from the molecular analyses were critical for reaching a final diagnostic conclusion of Ewing tumor–peripheral neuroectodermal tumor and hence had important therapeutic implications for the patient.