ATIM-18. A PHASE I TRIAL OF HYPOFRACTIONATED STEREOTACTIC IRRADIATION (HFSRT) WITH PEMBROLIZUMAB AND BEVACIZUMAB IN PATIENTS WITH RECURRENT HIGH GRADE GLIOMA (NCT02313272)

Abstract

There is strong pre-clinical evidence for the combination of PD-1 blockade with radiotherapy and anti-VEGF therapy. Herein, we present safety and efficacy data from a phase 1 study combining pembrolizumab, an anti-PD-1 monoclonal antibody, with hypofractionated stereotactic irradiation (HFSRT) and bevacizumab in recurrent high grade glioma. This phase I study (3 + 3 design) explored the safety, tolerability, recommended phase II dose (RP2D), and antitumor activity of pembrolizumab administered concurrently with HFSRT and bevacizumab. Adult patients with recurrent glioblastoma or anaplastic astrocytoma (maximum diameter of target lesion ≤ 3.5 cm) were eligible. Eligible patients received HFSRT to the recurrent tumor (30 Gy in 5 fractions) combined with bevacizumab (10 mg/kg, Q2W) and pembrolizumab (100 mg or 200 mg intravenously based on dose level, Q3W). Two dose levels of pembrolizumab were explored and 20 patients were treated at RPD2. Treatment continued until disease progression or unacceptable toxicity. Twenty three patients with recurrent glioblastoma have been treated on this study (3 patients at 100 mg and 20 patients at 200 mg dose levels). Five patients had previous tumor progression on bevacizumab. Combination of HFSRT with pembrolizumab (200 mg every 3 weeks) and bevacizumab was generally well tolerated. The most common toxicities were grade 1 fatigue and grade 1 proteinuria. No treatment-related neurologic adverse events were observed. In 1 patient, study treatment was discontinued due to grade 3 elevation of liver transaminases. Durable objective responses (complete response + partial response ≥ 6 months) were observed in 53% of patients. The overall survival rate (at the time of abstract submission) at 6 and 12 months were 94% (16 out of 17 patients) and 64% (7 out of 11 patients), respectively. Combination of HFSRT with pembrolizumab (200 mg every 3 weeks) and bevacizumab is safe. Clinical activity of this combination therapy is encouraging.