RESUMEN
Ewing sarcomas (ES) are rare small round cell sarcomas often affecting children and characterized by gene fusions involving one member of the FET family of genes (usually EWSR1) and a member of the ETS family of transcription factors (usually FLI1 or ERG). The detection of EWSR1 rearrangements has important diagnostic value. Here, we conducted a retrospective review of 218 consecutive pediatric ES at diagnosis and found eight patients having data from chromosome analysis, FISH/microarray, and gene-fusion assay. Three of these eight ES had novel complex/cryptic EWSR1 rearrangements/fusions by chromosome analysis. One case had a t(9;11;22)(q22;q24;q12) three-way translocation involving EWSR1::FLI1 fusion and 1q jumping translocation. Two cases had cryptic EWSR1 rearrangements/fusions, including one case with a cryptic t(4;11;22)(q35;q24;q12) three-way translocation involving EWSR1::FLI1 fusion, and the other had a cryptic EWSR1::ERG rearrangement/fusion on an abnormal chromosome 22. All patients in this study had various aneuploidies with a gain of chromosome 8 (75%), the most common, followed by a gain of chromosomes 20 (50%) and 4 (37.5%), respectively. Recognition of complex and/or cryptic EWSR1 gene rearrangements/fusions and other chromosome abnormalities (such as jumping translocation and aneuploidies) using a combination of various genetic methods is important for accurate diagnosis, prognosis, and treatment outcomes of pediatric ES.