In B-ALL, recurrent genomic subtypes are characterized by chromosomal aneuploidy, i.e., hyperdiploidy (>50 chromosomes) or hypodiploidy (<44 chromosomes), and by rearrangements: ETV6/RUNX1 fusion, TCF3/PBX1 fusion, BCR/ABL1 fusion, and KMT2A (MLL) rearrangement (Figure 2 and Table 2). The gene discussed is KMT2A; the disease is acute lymphoblastic leukemia.