Cryptic PML-RARα fusion resulting from interstitial insertion of RARα into PML on 15q (case no. 2; Table 1). (a) FISH analysis using ICRF PML 15.5 (green) and RARα 121 (red) cosmid probes. The RARα probe hybridized to two chromosome 17s of normal appearance, whereas 1 normal PML locus was observed on chromosome 15. The PML-RARα fusion was detected on 15q (yellow arrow). Localization of the fusion gene was confirmed by subsequent hybridization with a chromosome 15 centromere probe, shown in red in (b). (c) Chromosome 15 paint (red); chromosome 17 centromere probe (green). (d) Chromosome 17 paint (green); chromosome 15 centromere probe (red)