KMT2A and leukemia: Lineage switching of leukemias may also occur; for example, leukemia associated with the KMT2A/AFF1 fusion gene, which as described above, commonly presents as pediatric B cell precursor ALL, may also demonstrate an infant B/myeloid mixed phenotype or relapse with the original clone switching to AML [139,140,194,195,196,197,198,199].