Eighty bevacizumab-naive, recurrent glioblastoma patients randomized to pembrolizumab with bevacizumab (cohort A, n=50) or pembrolizumab monotherapy (cohort B, n=30)….Tumor immune markers were not associated with OS, but worsened OS correlated with baseline dexamethasone use and increased post-therapy plasma VEGF (cohort A) and mutant IDH1, unmethylated MGMT and increased baseline PlGF and sVEGFR1 levels (cohort B)...Pembrolizumab was ineffective as monotherapy and with bevacizumab for recurrent glioblastoma.