Ctim-31. clinical impact of adding pembrolizumab to standard of care chemoradiation in patients with newly diagnosed glioblastoma

Abstract BACKGROUND Standard of care (SOC) for newly diagnosed glioblastoma includes radiotherapy plus temozolomide followed by 6 adjuvant cycles monthly temozolomide per the Stupp protocol. We report the secondary objectives of a single arm phase 2 study evaluating the clinical impact of the addition of immune check point inhibitor pembrolizumab to this standard therapy. METHODS Patients with histopathology proven glioblastoma (WHO 4) eligible to receive SOC were prospectively enrolled to received pembrolizumab 200 mg iv every 3 weeks for up to 35 doses, progression, development of dose limiting toxicity or withdrawal of consent. Patients also receive ferumoxytol steady state MRI scans at baseline, 4 weeks after the last day of standard of care stereotactic radiosurgery or chemoradiotherapy, every 9 weeks thereafter until suspected radiographic progression, and then within 4 weeks from suspected radiographic progression. Primary endpoints of the study were to test the sensitivity and specificity of ferumoxytol steady state imaging for response assessment in this cohort. Secondary objective includes Progression free (PFS) and Overall survival (OS) and toxicity. PFS and OS were analyzed using Kaplan-Meier method. RESULTS A total of 52 patients (19 F, 33 M; 43 IHD wt and 9 IDH mu; 25 MGMT gene methylated, 27 unmethylated) were enrolled and included. At a median Follow up of 14.3 months, median PFS was 10.7 m (95% CI:8.1-12.6) and median OS was 14.4 m (95%CI: 12.5-16.9). Two grade 3 or higher toxicities (bullous dermatitis and Steven-Johnson syndrome) were attributed to pembrolizumab. CONCLUSIONS Although, the addition of pembrolizumab to SOC was well tolerated in most patients, this study did not see any meaning clinical benefit in PFS or OS with the addition of pembrolizumab in patients with newly diagnosed glioblastoma. Analysis for the primary imaging endpoint is ongoing.