The long existing dogma within MLL-r leukemia research that HOXA9 is consistently highly expressed in all MLL-r leukemias has been challenged by several recent studies indicating that HOXA9 per se might not be required for all MLL-rearranged pediatric and infant ALL leukemias [41, 42]. The gene discussed is KMT2A; the disease is acute lymphoblastic leukemia.