ABCG2 and cancer: Given that the tumor’s resistance to certain chemotherapeutic agents might be due to the overexpression of ABC-transporters regulating the efflux of chemotherapeutic drugs from cancer cells, we initially examined whether the expression of 3 major ABC-transporters (e.g., ABCB1, ABCG2 and ABCC1) was increased in PTX-resistant (Tx-R) cancer cells.