Acute myeloid leukemia (AML) with NPM1m—which accounts for approximately 30% of AML cases and AML or acute lymphoblastic leukemia (ALL) with KMT2Ar—and is present in 5–10% of cases, shares a common pathogenetic mechanism: the aberrant activation of the MEIS1–HOXA axis. This evidence concerns the gene MEIS1 and acute lymphoblastic leukemia.