The prognosis is even worse than that of patients having an EVI1 mutation alone and the 5-year event-free survival rate of t(3;21) patients is only 14%.32 In a chimeric knock-in mouse model, Runx1-Evi1 expression alone was sufficient to induce a megakaryoblastic leukemia in adult mice,71 while Runx1-Evi1 expression early during hematopoietic development was embryonically lethal around day E13.5. Here, MECOM is linked to adult acute megakaryoblastic leukemia.