ABCB1 and cancer: This phenomenon is known as multidrug resistance (MDR), which is often due to up-regulation of transmembrane protein drug-efflux pumps, including p-glycoprotein (P-gp) also known as ATP-binding cassette sub-family B member 1 (ABCB1), or multidrug resistance-associated protein 2 (MRP2, ABCC2) which can actively pump many anti-cancer drugs out of the cells, a process powered by ATP hydrolysis.