ABC transporters have been found to be relatively highly expressed in drug-resistant tumors and able to transport intracellular chemotherapeutic agents to the extracellular compartment by relying on the energy provided by ATP hydrolysis, thereby mediating the resistance of tumor cells to chemotherapeutic agents (Choi and Yu, 2014; Beis, 2015). Here, ABCG2 is linked to neoplasm.