Early in the definition of MPAL, chromosomal anomalies also encountered in some cases of acute myeloid (AML) or acute lymphoblastic (ALL) leukemia were recognized defining specific entities: MPAL with BCR-ABL1 and MPAL with KMT2A (formerly the MLL mixed lineage leukemia gene) rearrangements. The gene discussed is KMT2A; the disease is acute lymphoblastic leukemia.