ABCB1 and cancer: The drug efflux activity of P-glycoprotein (P-gp, a product of the mdr1 gene and an ABCB1 member of the ABC transporter family) represents a mechanism by which tumor cells escape death induced by chemotherapeutic agents, resulting in the development of MDR in cancer cells and causing them to become insensitive to a range of different cytostatic drugs [1,2].