ABCB1 and acute leukemia: The best-known resistance gene in leukemia patients that has been shown to be correlated to poor outcomes is mediated by the MDR1 gene.3,6 However, clinical investigations into the role of MDR1 have yielded inconsistent results that are difficult to interpret.14 In several papers, the expression of Pgp did not correlate with the multidrug resistance phenotype.9,21 Thus, alternative proteins such as MRP1 may also contribute towards resistance in acute leukemia cases.