PML-RARα fusion resulting from interstitial insertion of PML with associated chromosome 15-derived material into RARα on 17q (case no. 4; Table 1). (a) FISH analysis using ICRF PML (green) and RARα (red) cosmid probes. PML-RARα fusion gene was detected on 17q (yellow arrow), adjacent to RARα hybridization signal (red arrow). Splitting of the RARα- derived signal on der(17q) was indicative of insertion of PML and adjacent sequence into the genomic region covered by RARα cosmid 121. Localization of the PML-RARα fusion gene was confirmed by subsequent hybridization with a chromosome 17 centromere probe shown in green in (b). (c) Chromosome 15 paint (red) and chromosome 17 centromere probe (green), confirming insertion of chromosome 15-derived material into 17q. (d) Chromosome 17 paint (green), chromosome 15 centromere probe (red). Chromosome 17 paint remained localized to 17; der(17q) showed a region of absent signal corresponding to the inserted region of 15q shown in (c).