A Pilot Surgical Trial To Evaluate Early Immunologic Pharmacodynamic Parameters For The PD-1 Checkpoint Inhibitor, Pembrolizumab (MK-3475), In Patients With Surgically Accessible Recurrent/Progressive Glioblastoma

Inclusion Criteria: * Have histologically confirmed World Health Organization Grade IV malignant glioma (glioblastoma or gliosarcoma). Participants will be eligible if the original histology was low-grade glioma and a subsequent histological diagnosis of glioblastoma or variants is made. * Be willing and able to provide written informed consent/assent for the trial. * Be 18 years of age on day of signing informed consent. * Have a Karnofsky performance status (KPS) ≥ 70 (Appendix A). * Previous first line therapy with at least radiotherapy. * Be at first or second relapse. Note: Relapse is defined as progression following initial therapy (i.e., radiation ± chemotherapy). For participants who had prior therapy for a low-grade glioma, the surgical diagnosis of a high-grade glioma will be considered the first relapse. * Participants must have shown unequivocal evidence for tumor progression by MRI or CT scan. * Demonstrate adequate organ function as defined in Table 1, all screening labs should be performed within 14 days of registration. Table 1 Adequate Organ Function Laboratory Values * System Laboratory Value * Hematological * Absolute neutrophil count (ANC) ≥1,500 /mcL * Platelets ≥100,000 / mcL * Hemoglobin ≥9 g/dL or ≥5.6 mmol/L without transfusion or EPO dependency (within 7 days of assessment) * Renal * Serum creatinine OR Measured or calculated creatinine clearance (GFR can also be used in place of creatinine or CrCl) ≤1.5 X institutional upper limit of no…