The genetic alterations are specific of each ALL immunophenotype being for examples hyperdiploidy (50–67 chromosomes); hypodiploidy (44 chromosomes or fewer); BCR-ABL1, ETV6-RUNX1, or TCF3-PBX1 fusions; PAX5 or ETV6 mutations, MLL rearrangements, or intrachromosomal amplification of chromosome 21 (iAMP21) specific for B-ALL, whilst alterations in LMO2, TAL1, TAL2, TLX1, TLX2, or HOXA are characteristics of T-ALL (Pui et al., 2019a). The gene discussed is TCF3; the disease is precursor B-cell acute lymphoblastic leukemia.