Evaluation of Eflornithine Plus Temozolomide in Patients With Newly Diagnosed Glioblastoma or Astrocytoma

Inclusion Criteria: * Diagnosis of World Health Organization (WHO) G4 classified GBM, IDH-wildtype (patients with GBM) or G3 astrocytoma (IDH1 or 2 mutant; CDKN2A/B intact) per WHO 2021 tumor classification. * Completed external beam radiation therapy per standard of care. * Patients with GBM: Must have received at least 80% of planned daily doses of TMZ during chemoradiation. Patients with astrocytoma: Must have tolerated adjuvant TMZ treatment through at least 2 and not more than 4 cycles. * Adequate hematologic, renal, hepatic, and other organ function as indicated by hematology and serum chemistry testing. * Willing to abstain from intercourse or use acceptable contraceptive methods. * If taking corticosteroids, must be on a stable or decreasing dose. Exclusion Criteria: * Recent history of recurrent or metastatic cancer that could confound response assessments * Prior systemic chemotherapy other than temozolomide during external beam radiation therapy (for patients with GBM) or adjuvant temozolomide through up to 4 pre-study cycles (for patients with astrocytoma). * Prior Optune treatment. * Active infection or serious intercurrent medical illness. * Poorly controlled seizures. * Significant cardiac disease within 6 months of enrollment. * Poorly controlled diabetes. * Use of another investigational agent within 30 days of enrollment.