To bypass the embryonic lethality of the knock-in model and to study AML development, conditional transgenic mouse models were developed that express RUNX1/ETO in adult bone marrow progenitors either using CRE/LoxP mediated recombination [23,24] or express the fusion protein under the control of the tetracycline (Tet) promoter [25]. This evidence concerns the gene RUNX1 and acute myeloid leukemia.