In a pivotal randomized trial investigating the value of temozolomide added to radiotherapy in patients with glioblastoma, median survival in patients with methylated MGMT promoter increased from 15.3 months (95% CI 13.0–20.9) with radiotherapy alone to 21.7 months (17.4–30.4) with radiotherapy and temozolomide (hazard ratio [HR] 0.51, 95% CI 0.31–0.84). This evidence concerns the gene MGMT and glioblastoma.