ABCB1 and cancer: Among them, ABCB1 was highly expressed in almost all types of MDR cancers, such as adrenocortical, colon, breast, and kidney; and the contribution of ABCB1 to MDR has been proven for many drugs, including vincristine, doxorubicin (DOX), and 5-fluorouracil (5-FU) (Fojo et al., 1987) (Table 1).