ABCB1 and cancer: When the mechanisms of chemoresistance on most multi-drug resistance (MDR) cancers are classified into pump and non-pump resistance, the pump resistance, caused by membrane proteins such as P-glycoprotein (P-gp/MDR1/ABCB1)5, 6, 7, 8, 9, multidrug resistance protein (MRP, MRP-1/ABCC1)10, 11, 12, and breast cancer resistant protein (BCRP, ABCG2)8, deports drugs out of cells, whereas the non-pump resistance mainly activates the cell death defense via anti-apoptotic proteins such as BCL2, MCL1, and BCL-XL13, 14, 15, 16.