CPX-351 is a liposome formulation of cytarabine and daunorubicin in 5:1 molar ratio. CPX-351 has ex vivo activity against a broad range of hematologic malignancies. Consistent with clinical data, CPX-351 activity is retained in high-risk AML blasts. Ex vivo analysis of AML blasts with FLT3-ITD shows increased sensitivity to CPX-351. Ex vivo analysis identifies AML subgroups warranting further clinical investigation.