ABCB1 and cancer: Additionally, the upregulation of ATP‐binding cassette (ABC) transporters, including multidrug resistance protein 1 (MDR1), multidrug resistance‐associated protein 1 (MRP1), and breast cancer‐resistant protein (BCRP), in drug‐resistant cancer cells, analogous to their role in placental development, may facilitate chemotherapy efflux, further resulting in treatment resistance.