Synergistic effect of reirradiation and PD-1 inhibitors in recurrent high-grade gliomas.

105Background: To date, studies of single agent PD-1 or PDL-1 inhibitors in recurrent high-grade gliomas (HGG) have shown infrequent responses ( < 10%) and limited efficacy. Reirradiation is considered one of the standard salvage regimens for selected patients with recurrent gliomas but tumor responses are also infrequent ( < 5%). Radiotherapy counteracts the immunosuppressive tumor microenvironment by increasing MHC class I expression and enhancing tumor neoantigen presentation and has a significant synergistic effect with PD-1 inhibition in preclinical models of glioma. Methods: From December 2014 to June 2016, 20 patients (14 men, 6 women) with recurrent HGG were treated with the combination of reirradiation and PD-1 inhibitors. 18 patients had a glioblastoma, 1 anaplastic astrocytoma and 1 anaplastic oligodendroglioma. The median KPS at the start of this regimen was 70 (50 to 80). The median number of prior treatments for recurrent tumor was 2 (1-4), 100% had prior radaition, 95% prior temozolomide an...