ABCB1 and cancer: In addition to the well characterized ABCB1 [P-glycoprotein (P-gp)], responsible for the multidrug resistance phenotype of cancer cells [8], the bile salt export pump (ABCB11/BSEP) regulating the excretion of bile salts from the liver and multidrug resistance protein 3 (ABCB4/MDR3) translocating phosphatidylcholine, the ABCB subfamily contains seven half-transporters consisting of a single NBD and a TMD.