ABCB1 and cancer: Multidrug resistance (MDR) is a difficult problem in treating cancer; one cause of multidrug resistance is overexpression of P-glycoprotein (P- GP) in cells, which is encoded by the Multidrug Resistance 1 (MDR1) gene and acts as an efflux pump for various chemotherapeutics (Syed and Coumar, 2016).