ABCB1 and central nervous system cancer: Before drug treatments, the expression ratios of drug-resistant ABC transporters in glioma cells (ABCB1 = 0.50 ± 0.06, ABCC1 = 0.26 ± 0.10, and ABCG2 = 0.57 ± 0.01) were evidently lower than those in GSCs (ABCB1, ABCC1 or ABCG2 = 1, respectively).