The in vivo efficacy of sunitinib against ALL-2 contrasts with the lack of significant activity against ALL-3, a PDX that harbors a KMT2 A gene fusion and expresses high levels of FLT3 mRNA, suggesting that high FLT3 expression alone is not sufficient for in vivo activity of sunitinib. This evidence concerns the gene FLT3 and acute lymphoblastic leukemia.