RecruitingPhase 1Drug trialA Clinical Trial on Combined (Neo-)Adjuvant Intravenous Plus Intracranial Administration of Ipilimumab and Nivolumab in Recurrent GlioblastomaThe goal of this phase I interventional study is to determine the safety and feasibility of the proposed investigational (neo-)adjuvant treatment regimen in patients with resectable reccurent glioblastoma. Participants will: * receive neo-adjuvant administration of intravenous immunotherapy * followed by a maximal safe neurosurgical resection * afterwards, immunotherapy will be injected into the brain tissue * followed by insertion of an Ommaya reservoir * postoperatively, administration of immunotherapy will be continued