Using fluorescence in situ hybridization (FISH) on interphase nuclei or metaphases, we report here the characterization of particular karyotypes in Ewing tumors, namely a complex t(2;11;22) translocation, a variant t(12;22) translocation, and one Ewing tumor without specific rearrangements but with an EWS/ERG fusion gene demonstrated by molecular analysis.     ///    and (4) to show that the generation of an EWS/ERG fusion gene cannot be obtained through a simple balanced translocation..     ///    Multiple chromosomal mechanisms generate an EWS/FLI1 or an EWS/ERG fusion gene in Ewing tumors.. 