ABCG2 and cancer: Kunická T. and Souček P., (Kunická and Souček 2014) mentioned that resistance to multiple drugs has one of the most important causes of cancer treatment failure, ABC transporters are membrane-bound proteins that participate in cell defense mechanisms, hence their function is to prevent toxicity as carcinogenesis on the one hand, but may contribute to resistance of tumor cells to a number of drugs, including chemotherapeutics.