A Randomized Phase II/III Open-Label Study of Ipilimumab and Nivolumab Versus Temozolomide in Patients With Newly Diagnosed MGMT (Tumor O-6-Methylguanine DNA Methyltransferase) Unmethylated Glioblastoma

• PRIOR TO STEP 1 REGISTRATION:

• No known IDH mutation. (If tested before step 1 registration, patients known to have IDH mutation in the tumor on local or other testing are ineligible and should not be registered)

• Availability of formalin-fixed paraffin-embedded (FFPE) tumor tissue block and hematoxylin \& eosin (H\&E) stained slide to be sent for central pathology review for confirmation of histology and MGMT promoter methylation status. Note that tissue for central pathology review and central MGMT assessment must be received by the New York University (NYU) Center for Biospecimen Research and Development (CBRD) on or before postoperative calendar day 23. If tissue cannot be received by postoperative calendar day 23, then patients may NOT enroll on this trial as central pathology review will not be complete in time for the patient to start treatment no later than 6 weeks following surgery. Results of central pathology review and central MGMT analysis will generally be conveyed to NRG Oncology within 10 business days of receipt of tissue. Note: In the event of an additional tumor resection(s), tissue must be received within 23 days of the most recent resection and the latest resection must have been performed within 30 days after the initial resection. Surgical resection (partial or complete) is required; a limited biopsy is not allowed because it will not provide sufficient tissue for MGMT analysis

‣ Note: The central pathology review and central MGMT results determine eligibility. Therefore, patients may be offered the opportunity to consent REGARDLESS of local pathology and MGMT results, and consent can occur BEFORE local pathology interpretation is finalized and BEFORE local MGMT testing is conducted

• Contrast-enhanced brain MRI within 3 days after surgery

‣ MRI with Axial T2 weighted FLAIR {preferred} or T2 turbo spin echo (TSE)/fast spin echo (FSE) and 3-dimensional (3D) contrast-enhanced T1 sequences are required

⁃ 3D pre contrast-enhanced T1 sequences are strongly suggested

• Women of childbearing potential (WOCBP) and men who are sexually active with WOCBP must be willing to use an adequate method of contraception hormonal or barrier method of birth control; or abstinence during and after treatment

• The patient or a legally authorized representative must provide study-specific informed consent prior to study entry

• PRIOR TO STEP 2 REGISTRATION:

• Histopathologically proven diagnosis of glioblastoma (or gliosarcoma as a subtype of glioblastoma) confirmed by central pathology review

‣ Note: diagnoses of Molecular glioblastoma per the Consortium to Inform Molecular and Practical Approaches to Central Nervous System (CNS) Tumor Taxonomy (c-IMPACT-NOW) criteria or CNS grade 4 per the World Health Organization (WHO) 2021 criteria are NOT relevant

• MGMT promoter without methylation confirmed by central pathology review. Note: Patients with tissue that is insufficient or inadequate for analysis, fails MGMT testing, or has indeterminate or methylated MGMT promoter are excluded.

‣ Note: central pathology review and central MGMT results determine eligibility; local pathology or MGMT results cannot be used for eligibility/randomization

⁃ Note: patients with methylated MGMT may be considered for enrollment on NRG-BN011

• IDH mutation testing by at least one method (such as immunohistochemistry for IDH1 R132H) must be performed as part of standard of care and no mutation must be found (i.e IDH wildtype). (If a mutation is identified then the patient will be ineligible and must be registered as ineligible at step 2.)

‣ Note: this test is not being performed in real time as part of central review and will not be provided to sites from a centrally performed test

• History/physical examination within 28 days prior to step 2 registration

• Karnofsky Performance Status (KPS) \>= 70 within 28 days prior to step 2 registration

• Neurologic function assessment within 28 days prior to step 2 registration

• Age \>= 18 years

• Hemoglobin \>= 10 g/dl (Note: the use of transfusion or other intervention to achieve hemoglobin \[Hgb\] \>= 10.0 g/dl is acceptable) (within 7 days prior to step 2 registration)

• Leukocytes \>= 2,000/mm\^3 (within 7 days prior to step 2 registration)

• Absolute neutrophil count \>= 1,500/mm\^3 (within 7 days prior to step 2 registration)

• Platelets \>= 100,000/mm\^3 (within 7 days prior to step 2 registration)

• Total bilirubin =\< 1.5 x institutional/lab upper limit of normal (ULN) (within 7 days prior to step 2 registration)

• Aspartate transaminase (AST) (serum glutamic-oxaloacetic transaminase \[SGOT\]) =\< 2.5 x ULN (within 7 days prior to step 2 registration)

• Alanine transferase (ALT) (serum glutamate pyruvate transaminase \[SGPT\]) =\< 2.5 x ULN (within 7 days prior to step 2 registration)

• Serum creatinine =\< 1.5 x ULN OR creatinine clearance (CrCl) \>= 50 mL/min (if using the Cockcroft-Gault formula) (within 7 days prior to step 2 registration)

• For patients with evidence of chronic hepatitis B virus (HBV) infection, the HBV viral load must be undetectable on suppressive therapy, if indicated. Patients with a history of hepatitis C virus (HCV) infection must have been treated and cured. For patients with HCV infection who are currently on treatment, they are eligible if they have an undetectable HCV viral load

• For women of childbearing potential (WOCBP), negative serum or urine pregnancy test within 7 days prior to step 2 registration. Note that it may need to be repeated if not also within 3 days prior to treatment start

‣ Women of childbearing potential (WOCBP) is defined as any female who has experienced menarche and who has not undergone surgical sterilization (hysterectomy or bilateral oophorectomy) or who is not postmenopausal. Menopause is defined clinically as 12 months of amenorrhea in a woman over 45 in the absence of other biological or physiological causes