ABCB1 and acute lymphoblastic leukemia: Proximal promoter regulates the expression of MDR1 in normal tissues, including the liver, kidneys and adrenal glands, while the distal promoter triggers the expression of MDR1 in colchicine-selected (selected) cells [33,73], mononuclear cells of patients with acute lymphoblastic leukemia who overexpress MDR1 [74], and cells of the primary breast tumors [75].