Internal tandem duplications (ITD) in the receptor tyrosine kinase FLT3 occur in 25% of acute myeloid leukemia (AML) patients and lead to constitutive activation of FLT3, driving leukemia cell survival and proliferation. Quizartinib, crenolanib and gilteritinib are second-generation FLT3 inhibitors (FLT3i) in phase III trials or clinical use for the targeted treatment of FLT3-ITD+ AML. However, they demonstrated only limited benefit and were not curative. A full understanding of cellular resistance factors contributing to this poor response is lacking. Here, we examined cell-autonomous pathways modulated by FLT3i using global translatome and phosphoproteome proteomics to identify non-genetic resistance mechanisms.