MGMT Protein Expression and Promoter Methylation in Glioblastoma Survival: a systematic review and meta-analysis

BACKGROUND: Glioblastoma is the most common malignant brain tumor in adults. Methylation of the O6-methylguanine-DNA methyltransferase (MGMT) promoter is the only clinically used biomarker predicting response to alkylating agents such as temozolomide and is associated with improved survival. However, its predictive accuracy is limited by an intermediate gray zone and variability in assessment methods. To reduce overtreatment of patients, improved stratification strategies are needed, potentially through integration of additional biomarkers such as MGMT protein expression. METHODS: We performed a systematic review to evaluate studies comparing the prognostic value for progression-free survival and overall survival of MGMT promoter methylation and MGMT protein expression in glioblastoma patients treated with temozolomide, including 33 independent cohorts with a total of 4,691 patients. We searched three databases up to May 2025. Risk of bias was assessed with a modified Quips tool. RESULTS AND DISCUSSION: Methylation-specific PCR and pyrosequencing indicated stronger prognostic value than immunohistochemical assessment of MGMT protein expression with hazard ratios (HRs) of 2.07 (95%CI 1.61-2.66), 2.13 (95%CI 1.64-2.75), and 1.50 (95%CI 1.26-1.79), respectively. An inverse correlation between MGMT promoter methylation and protein expression was observed in only 52% of assessed studies, suggesting that promoter methylation and protein expression may contribute independently to prognosis. CONCLUSION: Substantial variability in methylation assays and protein cut-offs underscores the need for methodological harmonization in future studies and clinical practice. Integration of MGMT protein expression with promoter methylation refines identification of primary temozolomide-resistant tumors and supports the debate of withholding temozolomide in patients unlikely to benefit.