Recent preclinical studies indicate that FLT3-ITD–mutated AML cells are rescued from FLT3 inhibition due to bone marrow microenvironment–mediated factors including stromal cells, involving direct cell-cell contact and soluble factors, as well as hematopoietic cytokines and growth factors (e.g., FLT3 ligand, AXL, IL-3, GM-CSF, and FGF2) (25–29). This evidence concerns the gene AXL and acute myeloid leukemia.