This is a phase 2 study for patients that have been diagnosed with recurrent glioblastoma, a type of brain cancer. This study is testing an investigational combination of two drugs, reltalimab and nivolumab."Investigational" means it has not been approved by the United States Food and Drug Administration (FDA). The main purpose of this study is to see if there is a difference in overall survival rate in patients who receive a combination of retatlimab and nivolumab versus those who receive the standard of care treatment, lomustine, in patients with recurrent brain cancer. Participants in this study can expect to be in this study for up to five years from the day study participation starts. Subjects with investigational project being given on day 1 of each cycle, a cycle being 28 days. Cycles will continue until disease gets worse or study doctor decides it is in the subject's best interest to stop. Study will be divided into group 1 and 2. Group 1 will receive investigational drugs and group 2 will receive the standard of care. A computer will be used to assign groups in a process called randomization. Much like a toss of a coin, subjects will have equal opportunity to randomized to either group 1 or 2.

Glioblastoma adaptive, global, innovative learning environment or GBM AGILE trial is to identify effective therapies and improve survival for a type of brian cancer called glioblastoma (GBM) and to match effective therapies with adult patients with newly diagnosed or recurring glioblastoma. Eligible participants will have a 50/50 chance of taking either standard therapy medications or a medication not yet approved by the FDA called regorafenib during their standard of care treatment for GBM.