In particular, the three ABC transporters P-glycoprotein (MDR1, ABCB1/MDR1), multidrug resistance-associated protein 1 (ABCC1/MRP1), and breast cancer resistance protein (ABCG2/BCRP) play a crucial role in the translocation of a broad range of drugs, such as several chemotherapeutic agents [2]; their overexpression is one of the mechanisms responsible for the development of multiple drug resistance by cancer cells [3]. Here, ABCG2 is linked to cancer.