Based on promising laboratory data, the MecMeth study is the first to bring a combined temozolomide/meclofenamate therapy into clinical use in patients with relapsed MGMT-promoter-methylated glioblastoma. Meclofenamate disrupts therapy resistance-mediating tumor cell networks and thus makes tumor cells more sensitive to chemotherapy. In phase 1, the optimal dose of meclofenamate in combination with temozolomide will be determined, which will then be investigated in a randomized phase 2 for initial indications of improved efficacy. A maximum of 12 patients will be included in Phase 1; Phase 2 consists of two parallel groups of 30 patients each.