Semaxanib (SU5416) is another TKI that targets VEGFRs and KIT (Fong et al., 1999; Smolich et al., 2001), but with additional activity against FLT3: a cytokine receptor mutated in ∼30% of AML patients, resulting in constitutive signaling activation and a highly proliferative, poor prognosis leukemia (Yee et al., 2002). The gene discussed is KIT; the disease is acute myeloid leukemia.