RUNX1 and acute myeloid leukemia: While the literature has described a second hit as necessary for development of leukemia in the presence of RUNX1-RUNX1T1 [12, 34–39], our findings confirm the reported RUNX1-RUNX1T1 dependence of AML t(8;21) cells for sustaining the leukemic cell population [13–15, 40].