FLT3 and acute myeloid leukemia: CD123 is the α-chain of IL-3 receptor (34), overexpressed on stem/progenitor CD34+/CD38− AML cells (35, 36), associated with increased cycling activity, low CD34-high CD11b-highCD14 expression, increased cellularity at diagnosis, hypersensitivity to IL-3 stimulation and poor prognosis, as well as frequently associated with FLT3-ITD mutations (37–40).