Several subtypes of childhood B-ALL have been shown to arise in utero including those characterized by KMT2A-r (103, 104), ETV6-RUNX1 (105–107), BCR-ABL (108), TCF3-PBX1 (109), TCF3-ZNF384 (110) gene fusions and high hyperdiploid ALL (111, 112) (Figure 2). Here, TCF3 is linked to precursor B-cell acute lymphoblastic leukemia.