FOXO3 and leukemia: • Bim expression is downregulated in Bcr-Abl+ leukemia cells.• STI571 increases FoxO3a-dependent transcription of Bim, which was shown to be important for apoptosis.• Imatinib induces the expression of hypophosphorylated BimEL in K562 and BV173 chronic myelogenic leukemia cells.• Bim knockdown reduced susceptibility to imatinib-induced apoptosis.• Imatinib induces apoptosis of c-Kit-dependent gastrointestinal stromal tumor cells.