FISH may be used to detect rearrangement of the most commonly rearranged genes in Ph-like ALL for which targeted therapies are currently available (e.g., ABL-family kinase genes, CRLF2, NTRK3) with caveats—for example, the focal insertions of EPOR into IGH and similar enhancer regions are not robustly detected by FISH due to the small size of the EPOR insertion. This evidence concerns the gene CRLF2 and acute lymphoblastic leukemia.