FLT3 and acute promyelocytic leukemia: Arsenic trioxide (ATO), one of the key drugs in treating acute promyelocytic leukemia and which induces differentiation of leukemic cells by enhancing RARA gene function, in combination with the FLT3 inhibitors showed a synergistic anti-leukemic effect in vivo along with reduced expression (or facilitated poly-ubiquitination) of FLT3 proteins [27].