Finally, in order to evaluate the underlying mechanism of this drug combination, we detected three drug-resistance genes, including ABCB1 (P-glycoprotein, P-gp), ABCC1 (multidrug-resistance protein 1, MRP1) and ABCG2 (mitoxantrone-resistance protein, MXR), which are the most clinically significant ABC transporters that cause multidrug resistance during cancer therapy [35,36]. This evidence concerns the gene ABCG2 and cancer.