Hypofractionnated stereotactic radiotherapy and anti-PDL1 durvalumab combination in recurrent glioblastoma: Results of the phase I part of the phase I/II STERIMGLI trial.

2046Background: Glioblastoma (GBM) is the most aggressive primary brain tumor with inevitable local relapse and no standard treatment. Hypofractionated stereotactic radiotherapy (hFSRT) has shown signs of efficacy with tolerable safety with PFS ranging from 3.4 to 5 months, but needs improvement. Radiotherapy (RT) causes immunogenic tumor cell death but also induces PDL1 and PD1 expression on tumors and immune cells, potentially evoking resistance to RT. Pre-clinical studies combining hFSRT with an anti-PD-1 antibody in GBM have shown increased efficacy of the combination. Clinical studies also show encouraging results when checkpoint inhibitors have been combined with high dose RT. We hypothesized that combining the anti PD-L1 Durvalumab (Durva) with hFSRT will be an effective regimen for patients with recurrent GBM. We designed a phase I and a phase II clinical trials studying the combination of hFSRT with Durva for recurrent GBM≤35 mm diameter. Results of the phase I are presented. Methods: A standard ...