MGMT and glioblastoma: MGMT promoter methylation in newly diagnosed GBM patients was also associated with improved OS and PFS (OS: HR = 0.49, 95% CI 0.43–0.57, p < 0.001, I2 = 87.7%; PFS: HR = 0.50, 95% CI 0.41–0.61, p < 0.001, I2 = 73.8%, Figure S2 in Supplementary Material).