Upregulation of drug efflux ATP-binding cassette (ABC) transporters, such as P-glycoprotein (P-gp), multidrug resistance protein 1 (MRP1), and breast cancer resistance protein (BCRP), may be responsible for the resistance to many chemotherapeutics affecting disposition of these drugs in the tumour cells and modifying seriously the clinical outcome [1, 20, 22, 23]. The gene discussed is ABCB1; the disease is neoplasm.