FLT1 and acute myeloid leukemia: THP-1, a human FLT3 wild-type (FLT3/WT) cell line, HL-60, a human AML cell line with minimal level of FLT3/WT expression and no response to FLT TKI, as well as U937 cells, a cell line lacking FLT3 expression, were used as controls.