ABCG2 and breast cancer: Of note, TNBCs are more likely to overexpress multi-drug-resistant protein-1 (ABCC1/MRP1), multi-drug-resistant protein–8 (ABCC11/MRP8), and the breast cancer resistance protein (ABCG2/BCRP) compared to other breast cancer subtypes [20, 22, 23], which may contribute to poor response to chemotherapy.