MGMT and glioblastoma: Following pooling results in random-effects model, the GBM patients with methylated MGMT promoter had a significantly longer PFS (HR = 0.56, 95 % CI = 0.32–0.80) compared with un-methylated MGMT promoter with statistic heterogeneity (I = 80.6 %, p = 0.001) (shown in Fig. 4).