The best characterized mechanism of MDR is the overexpression of ATP-binding cassette (ABC) transporters in cancer cells4,5, including P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), and MDR-associated protein 1 (MRP1), which function as drug pumps that efflux drugs out of cells3,6,7. Here, ABCB1 is linked to cancer.