Multidrug resistance protein-1 (MDR1) has been proven to be associated with the development of chemoresistance to imatinib (Glivec, STI571) which displays high efficacy in treatment of BCR-ABL-positive chronic myelogenous leukemia (CML). This evidence concerns the gene ABCB1 and chronic myelogenous leukemia, BCR-ABL1 positive.