In accordance with the two-hit hypothesis [2] of leukemic transformation, FLT3-ITD expression in mouse bone marrow cells expressing a promyelocytic leukemia (PML)/retinoic acid receptor (RAR) α fusion protein of acute promyelocytic leukemia (APL) caused accelerated malignant transformation[3]. This evidence concerns the gene FLT3 and acute promyelocytic leukemia.