ABCG2 and breast carcinoma: To the best of our knowledge, evidence for mitochondrial MDR efflux pumps is limited to those in the human breast carcinoma cell line MCF-7S, which displays doxorubicin (DOX) resistance linked to the ABC mitochondrial drug efflux pump, breast cancer resistance protein BCRP1 (ABCG2) and the MDR-associated protein MRP1 (ABCC1 [41].