ABCB1 and acute myeloid leukemia: AML appears to be maintained by a pool of self-renewing leukemia stem cells (LSCs) that are typically characterized by a CD34+CD38−CD123+ immunophenotype.15 AML stem cells are highly resistant to chemotherapy since they are primarily in the G0 phase of the cell cycle and preferentially express multiple drug-resistant proteins such as P-glycoprotein and Bcl-2.16,17 The persistence of these LSCs predisposes to relapse even if bulk AML cells are effectively eliminated by treatment.