Identification of High-risk Cryptic CRLF2 Rearrangements in B-Cell Acute Lymphoblastic Leukemia Utilizing an FGFR3/IGH Dual-Color Dual-Fusion DNA Probe Set

B-cell acute lymphoblastic leukemia (B-ALL) is the most common childhood malignancy with gene rearrangements involving the IGH locus occurring in ∼5% of cases. Fluorescence in situ hybridization (FISH) probes targeting the IGH locus are not included in the standard children’s oncology group (COG) fluorescence in situ hybridization panel. At our institute, we incorporated the use of FGFR3/IGH dual-color dual-fusion DNA probes for confirmation of aneuploidy 4 and 14 in diagnostic B-ALL specimens. Subsequently we have identified 4 B-ALL cases with cryptic CRLF2-IGH translocations that would otherwise have gone undetected. Detection of genetic alterations in B-ALL, such as CRLF2 rearrangements, may enhance patient risk stratification and therapy options in pediatric B-ALL.