Rearrangements involving KMT2A and its fusion partner genes are found in precursor B-cell acute lymphoblastic leukemia (B-ALL), T-ALL, AML, myelodysplastic neoplasm (MDS), mixed-lineage (biphenotypic) leukemia (MPAL), and secondary leukemia [1,2,3]. The gene discussed is KMT2A; the disease is acute lymphoblastic leukemia.