Retifanlimab With or Without Difluoromethylornithine for the Treatment of Progressive High Grade Gliomas

Inclusion Criteria: * Age ≥ 18 years * Diagnosis of high-grade glioma, including any of the following: * Glioblastoma, IDH-wild type (WT) * Grade 3 or 4 IDH1/2 mutant astrocytoma or * Grade 3 oligodendroglioma * Any prior grade 2 astrocytoma or oligodendroglioma that is suspected to have recurred at a higher grade * Other high-grade glioma * Plan for surgical resection as part of routine clinical care * Radiographic disease progression, with or without tissue confirmation * Measurable disease * Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0, 1 or 2 and Karnofsky Performance Status (KPS) ≥ 60 * NOTE: PS must be assessed (again) within 7 days prior to first dose of study drug * Hemoglobin ≥ 9.0 g/dL (obtained ≤ 15 days prior to registration) * Absolute neutrophil count (ANC) ≥ 1500/mm\^3 (obtained ≤ 15 days prior to registration) * Platelet count ≥ 100,000/mm\^3 (obtained ≤ 15 days prior to registration) * Total bilirubin ≤ 1.5 x upper limit of normal (ULN) (obtained ≤ 15 days prior to registration) * Alanine aminotransferase (ALT) and aspartate transaminase (AST) ≤ 3 x ULN (≤ 5 x ULN for patients with liver involvement) (obtained ≤ 15 days prior to registration) * Calculated creatinine clearance ≥ 45 ml/min using the Cockcroft-Gault formula (obtained ≤ 15 days prior to registration) * Negative pregnancy test done ≤ 7 days prior to registration, for persons of childbearing potential only * Provide written informed consent for the current s…