The small molecule TKI sunitinib (c-kit, flt-3, VEGFR2, PDGFR-beta inhibition) is noted to have cardiac toxicity as a DLT in a pediatric solid tumor phase I study, while sorafenib (c-kit, flt-3, VEGFR2, PDGFR-beta, and RaF-pathway inhibition) has completed phase I testing in children with leukemia without this toxicity (24, 25). Here, FLT3 is linked to leukemia.