Surgical Pembro +/- Olaparib w TMZ for rGBM

This is an open label, multi-center, phase II trial evaluating the safety and efficacy of olaparib, temozolomide and pembrolizumab in participants with recurrent glioblastoma at their first or second relapse. The U.S. Food and Drug Administration (FDA) has not approved pembrolizumab or olaparib for recurrent glioblastoma, but both have been approved for other uses. Pembrolizumab is an antibody designed to block the action of the receptor, PD-1. PD-1 works to help tumor cells inhibit the immune system's response against a tumor. Olaparib is an inhibitor of PARP (poly \[adenosine diphosphate-ribose\] polymerase) an enzyme found in the cells of the human body that helps cells, including cancer cells, survive and grow by repairing DNA damage in the cells. Olaparib helps kill cancer cells by preventing PARP from repairing their DNA. The U.S. FDA has approved temozolomide as a treatment option for glioblastoma. Temozolomide is a chemotherapy drug that can enter the brain and prevent tumor cells from growing by causing DNA damage. The research study procedures include screening for eligibility and study treatment including evaluations and follow up visits. It is expected that all participants will receive pembrolizumab for up to 2 years or as long as they do not have serious side effects and their disease does not get worse. It is expected that Cohort 1 and Cohort 2 Arm A participants will receive Olaparib and temozolomide for as long as they do not have serious side effects and their disease does not get worse. It is expected that about 66-78 people will take part in this research study. Merck Sharp \& Dohme Corp., a subsidiary of Merck \& Co., Inc., is supporting this research study by providing funding for the research study and both investigational study drugs, pembrolizumab and olaparib.