KMT2A and leukemia: Gene rearrangements involving MLL, termed MLLr, are among the most potent oncogenic drivers of leukemia detected in over 70% of acute lymphoblastic (ALL), up to 50% of acute myeloid leukemia (AML) cases in infants [1,2,3,4] and approximately 10% of adult leukemia including refractory therapy-related cases [5,6,7,8].