Study of Silevertinib With Temozolomide for the Treatment of Newly Diagnosed GBM With Unmethylated MGMT and EGFRvIII

The purpose of this study is to see if combining silevertinib with temozolomide after surgery and radiotherapy helps treat newly diagnosed glioblastoma (GBM) better than using temozolomide alone in the maintenance setting. Specifically, this study is being done to find answers to the following questions: * How much of the study drugs (silevertinib combined with temozolomide) should be given to participants with GBM? * What are the side effects participants have when taking the study drug (silevertinib combined with temozolomide)? * Can the study drug (silevertinib combined with temozolomide) help participants with GBM live longer without disease progression compared to treatment with temozolomide alone?

Key Inclusion Criteria: * Newly diagnosed histologically confirmed glioblastoma that is isocitrate dehydrogenase wild type (IDH-WT). * Positive EGFR status in the brain tumor as determined by a commercially available test or validated laboratory assay (CLIA or comparable certification). * For Part 1 (Safety Lead-in) ONLY: EGFR alterations. * For Part 2 (Randomized, Controlled Trial) ONLY: EGFRvIII. * For Part 2 (Randomized, Controlled Trial) ONLY: Unmethylated MGMT promoter tumor status based on a validated assay. * No treatment for newly diagnosed GBM other than surgery followed by standard-of-care adjuvant postoperative radiation (54 to 60 Gy) and TMZ chemotherapy. * At least 4 weeks since completion of radiation therapy, with a post-radiation MRI showing no progression. Key Exclusion Criteria: * Recurrent multifocal disease, metastatic, leptomeningeal, or extracranial GBM, or gliomatosis cerebri. * Progression of GBM prior to Enrollment, Screening, or Randomization. * Biopsy-only/no resectional surgery. * Prior or concomitant treatment for GBM with an EGFR-targeting agent, including silevertinib, bevacizumab, cytotoxic chemotherapy, immunotherapy, experimental therapies, Gliadel wafers, GammaTile®, or other intratumoral or intracavitary antineoplastic therapy. * Intent to use Optune® (TTF). * Significant other uncontrolled health conditions or other malignancies.