FLT3 and acute myeloid leukemia: To test whether FLT3-ITD and p53 haploinsufficiency or loss cooperate to initiate AML, we crossed FLT3-ITD knock-in mice [17] with p53 knockout mice [18] to generate mice harboring both ITD/ITD (FLT3-ITD homozygous) and p53 knockout mutations (Fig. 1a).