Although in several studies MRP1 has been shown to be involved in multidrug resistance,22,23 in other investigations MRP1 expression appeared to have no impact on treatment outcome in AML cases.24-26MRP1 has been detected in a wide variety of solid and hematological tumors, but evaluation of the presence of MRP1 protein or its cognate mRNA in a tumor sample is complicated by the fact that the MRP1 gene is expressed in the tissue from which these tumors originate and the protein is also expressed in all lineages of normal hematopoietic cells. This evidence concerns the gene ABCC1 and acute myeloid leukemia.