FLT3 and acute myeloid leukemia: The primary AML cells, being isolated from 4 relapsed patients (Case #3 and #5 with FLT3-ITD mutation, case #4 with FLT3-ITD + D835Y mutation, and case #6 without FLT3 mutation at relapse) were truly resistant to sorafenib in vitro (Fig. 1A–D).