OS4.4 Hypofractionated stereotactic radiotherapy and anti-PDL1 Durvalumab combination in recurrent glioblastoma: Results of the phase I part of the phase I/II STERIMGLI trial

Abstract

Abstract BACKGROUND Glioblastoma (GBM) remains a lethal disease with inevitable local relapse and no standard treatment. Re-irradiation by hypofractionated stereotactic radiotherapy (hFSRT) is an option of treatment with tolerable safety, but needs improvement in term of efficacy. 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/II clinical trial studying the combination of hFSRT with Durva for recurrent GBM≤35 mm diameter. Results of the phase I are presented. MATERIAL AND METHODS Patients were included from February 2017 to October 2017. A standard 3 + 3 de-escalation design was used. Patients were treated by hFSRT 24 Gy, 8 Gy/fraction at 80% isodose, every other day, combined with Durva infusion 1500mg first dose (Level 1) or 750 mg (Level -1) delivered on the last hFSRT day followed by 1500 mg Durva infusion every four weeks until relapse. The schema was defined as safe if one patient or less among 6 presents a dose limiting toxicity (DLT). Brain MRI was performed before RT and then every 8 weeks until relapse. Tumor assessment was performed according to RANO criteria. RESULTS Among the 6 patients (3 methylated MGMT, 3 unmethylated MGMT; all wild type IDH) included at the level 1, all completed the hFSRT course, only one had a DLT which was an immune related grade 3 vestibular neuritis. At the time of analysis (24/01/19), all the patients had a local tumor progression, 4 were still alive. Local progression free interval (LPFI) ranges from 2.1 to 8.1 months. Interestingly the 2 patients who presented a pseudo-progression had a prolonged LPFI (5.7 and 8.1 months) compared to the other patients. All the patients except these 2 patients had a lymphopenia at inclusion. PDL-1 expression varied from 0 to 70% in the primary tumor. CONCLUSION Combining three 8 Gy fractions of hFSRT with 1500 mg Durvalumab on the 3rd fraction hFSRT and every 4 weeks for recurrent GBM is well tolerated justifying exploration of its efficacy in the phase II which is currently in interim analysis