In phase one of this multicenter national study, IH, MS-PCR, MethyLight, pyrosequencing and MS-HRM will be compared in a retrospective study on 100 samples (frozen for molecular analysis and paraffin-embedded for IH), taken from patients treated according to the Stupp protocol and with a follow-up of 18 months at least. In phase 2, the two techniques with the best cost/efficacy ratio (based on predictive value, analytical quality and feasibility of the test) will be implemented in all the laboratories according to a standard protocol developed by the referral centre for the tests. The dissemination of quality controls will allow us to check that the same results are obtained from one laboratory to another. In phase 3, samples will be analysed prospectively in the different centres and a medico-economic analysis will be undertaken on the integration of MGMT analysis into the standard care of GBM patients. Two types of analysis will be performed: i) on the costs of the techniques, allowing us in particular to estimate the possible additional clinical cost generated and its effect on the cost of a hospital stay, in order to adjust the charging system, and ii) on alternative care strategies for the patients, with or without screening, leading to improve the target of treatments by TMZ, with the aim of improving the definition of "options and recommendations" (cost-utility analysis).