PGP and cancer: ABCB1 (also known as the P-glycoprotein 1 [P-gp]), a member of the ATP-binding cassette (ABC) superfamily of transporters and encoded by the multidrug resistance 1 (MDR1) gene, is closely associated with drug resistance in a plethora of cancers because it pumps many foreign substances such as cytotoxic drugs out of cells [21, 22].