Currently, it is recognized that the main role in multi-drug resistance of cancer cells in vitro is played by ABCB1 (P-gp), ABCC1 (MRP1), ABCC2 (MRP2), ABCC4 (MRP4), ABCG2 (BCRP) and lung resistance protein (LRP) [37]. This evidence concerns the gene ABCG2 and cancer.