Background: The standard treatment for patients with newly diagnosed glioblastoma comprises maximum safe surgery, radiotherapy (RT), and concomitant and up to six cycles of maintenance temozolomide (TMZ) chemotherapy (TMZ/RT→TMZ). Despite this intense therapy, the prognosis remains poor and there is an urgent need to develop new therapeutic options. Marizomib is a novel, irreversible and brain-penetrant pan-proteasome inhibitor. Following its successful assessment in phase I trials in patients with newly diagnosed as well as recurrent glioblastoma, marizomib is now being investigated in a phase III trial. Methods: EORTC 1709/CCTG CE.8 is a multicenter, randomized, controlled, open label phase III superiority trial. Eligibility criteria include histologically confirmed newly diagnosed glioblastoma and a performance status ≥70. Approximately a total of 750 patients will be enrolled and randomized 1:1. Stratification factors include institution, age, Karnofsky performance status and extent of surgery. The primary objective of this study is to compare overall survival in patients receiving marizomib in addition to standard of care (TMZ/RT→TMZ) with patients receiving standard treatment only. The testing strategy specifies the determination of this objective in both the intent-to-treat population and the subgroup of patients with tumors harboring an unmethylated MGMT promoter. Secondary endpoints include progression-free survival, safety, neurocognitive function and quality of life. The study is accompanied by a translational research program. The study will be opened at 50 EORTC sites in Europe and done as an intergroup collaboration with the Canadian Cancer Trials Group (CCTG) with 25 sites in Canada and additional sites in the US. Patient enrolment started in June 2018 and as of January 29, 2019, a total of 85 patients have been randomized. An update on the enrolment status will be provided at the ASCO conference. Clinical trial information: NCT03345095