Testing the Combination of Anti-cancer Drugs Tiragolumab and Atezolizumab to Improve Outcomes for Patients With Recurrent Glioblastoma

Inclusion Criteria: * Patients must have histologically confirmed IDH wildtype World Health Organization (WHO) grade IV glioblastoma at first or second relapse * Documented progression of disease as defined by modified Response Assessment in Neuro-Oncology (mRANO) criteria at least 12 weeks after completion of radiotherapy, unless the recurrence is outside the radiation field or has been histologically documented * Age ≥ 18 years. Because no dosing or adverse event data are currently available on the use of atezolizumab in combination with tiragolumab in patients \< 18 years of age, children are excluded from this study * Eastern Cooperative Oncology Group (ECOG) performance status \< 2 (Karnofsky ≥ 60%) * Leukocytes ≥ 2,000/mcL * Lymphocyte count ≥ 500/mcL * Absolute neutrophil count ≥ 1,500/mcL without granulocyte colony-stimulating factor support * Platelets ≥ 100,000/mcL without transfusion * Hemoglobin ≥ 9 g/dL * Total bilirubin ≤ 1.5 x institutional upper limit of normal (ULN) (however, patients with known Gilbert disease who have serum bilirubin level ≤ 3 x ULN may be enrolled) * Aspartate aminotransferase (AST)(serum glutamic oxaloacetic transaminase \[SGOT\])/alanine aminotransferase (ALT)(serum glutamic pyruvic transaminase \[SGPT\]) ≤ 2.5 x institutional ULN or ≤ 5 x ULN for patients with liver metastases * Alkaline phosphatase ≤ 2.5 x ULN (≤ 5 x ULN for patients with documented liver or bone metastases) * Glomerular filtration rate (GFR) ≥ 30 mL/min * Internation…