• H Pinson, G Hallaert, J Van der Meulen, F Dedeurwaerdere, D Vanhauwaert, C Van den Broecke, J Van Dorpe, D Van Roost, J P Kalala, and T Boterberg.
• Department of Neurosurgery, Ghent University Hospital, C. Heymanslaan 10, 9000, Ghent, Belgium. harry.pinson@ugent.be.
• J. Neurooncol. 2020 Jan 1; 146 (1): 55-62.

IntroductionQuantitative methylation specific PCR (qMSP) is a frequently used technique to assess MGMT gene promoter methylation in glioblastoma patients. The optimal technical cut-off value to distinguish methylated from unmethylated samples is nevertheless still undetermined. In literature, a "grey zone" of diagnostic uncertainty has been described.MethodsWe performed a retrospective analysis of newly diagnosed glioblastoma patients treated according to the Stupp protocol. Epidemiological data were gathered from the individual patient files. MGMT gene promoter methylation status was determined on stored tumour samples using qMSP. A strong, weak or absent promoter methylation was determined based on Cq values (quantification value) of the MGMT and ACTB primers as well as a positive control sample.ResultsIn total, 181 patient files were reviewed and included for statistical analysis. MGMT promoter hypermethylation was detected in 38.7% of glioblastoma patients. The median overall survival of unmethylated and strongly methylated patients was 10.1 months and 19.7 months respectively. Furthermore, 11% of the total patient cohort had a weak MGMT gene promoter methylation. The median OS in this subgroup was 15.4 months, significantly better compared to the unmethylated cohort (P < 0.001). Multivariate Cox regression analysis showed weak MGMT promoter methylation as an independent prognostic parameter for overall survival.ConclusionGlioblastoma patients with weak promoter methylation show a statistically significant longer overall survival when compared to clearly unmethylated patients. Patients with grey zone qMSP test results should receive additional molecular analysis in future to further direct individual therapy strategies.

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