ABCB1 and acute myeloid leukemia: Furthermore, for a subset of AML we determined ABCB1 activity and CD34/CD38 staining showing that the MDR phenotype is associated to a hematopoietic stem cell phenotype as it is known that the expression of ABCB1 correlates with the expression of CD34, a characteristic marker of the immature subset in AML blast cells [24].