Patient 1, with FMS-like tyrosine kinase 3 internal tandem duplication–positive FLT3-ITD+) AML, attained a morphologic leukemia-free state with clearance of some of the pathogenic mutations present at the time of post–haplo-HCT relapse but had a persistent FLT3-ITD mutation on day +28 bone marrow assessment. This evidence concerns the gene FLT3 and leukemia.