Probe schematic. Two strategies were used to detect FIP1L1-PDGFRA fusion at chromosome 4q12. The first strategy used a 2-color FISH approach with probes covering the CHIC2 locus at 4q12 that is direct-labeled with Spectrum Orange and a control probe covering the FGFR3 locus at 4p16.3 that was labeled in Spectrum Green (A). The second strategy used a break-apart FISH approach with 2 probes that both partially cover the CHIC2 locus and completely cover either the flanking FIP1L1 (labeled with Spectrum Orange) or PDGFRA (labeled with Spectrum Green) loci (B).