The role of Pgp in inducing MDR has been confirmed by in vitro studies.6 However, trial usage of Pgp modulators in leukemia has produced controversial results7 and it seems that MDR1 function in acute myelogenous leukemia (AML) patients does not correspond to in vitro drug resistance.8 In several studies on drug-resistant cell lines with increased drug efflux, no significant MDR1 expression was observed.9 In addition, the kinetics of anthracycline transport by MDR1 and MRP1 are very similar.10 This suggests that alternative proteins, such as MRP1, may play a role in the MDR phenotype.11 This evidence concerns the gene PGP and leukemia.