ABCG2 and central nervous system cancer: In contrast, as an effective way to alleviate a hypoxic environment, hyperoxia promotes the sensitivity of glioma cells to TMZ by decreasing the expression of MGMT, ABCG2 and Ki67 and inducing a higher cell apoptosis rate, resulting in an extended survival time for glioma patients15, 16, 18, 19, 32.