In a homogeneously pre-treated, mostly chemotherapy-naïve sample of 63 patients suffering from recurrent IDH wildtype GBM, outcome analysis revealed a survival benefit for patients treated with BCNU at 1st tumor relapse since survival after relapse was significantly prolonged compared to control patients (BCNU: 266 days; control: 187 days; p = 0.02). Here, IDH1 is linked to glioblastoma.