Study drug will be administered twice daily for 7 days prior to the initiation of RT (radiation therapy)and will continue twice daily during the course of RT. The RT schedule will be once daily for 5 days per week for 6 weeks (total radiation dose of 60 Gy. Oral temozolomide will be administered once daily (7 days per week) for the duration of RT. Four weeks after the completion of the course of RT, patients will be started on once-daily adjuvant temozolomide (Day 1-5 of a 28 day cycle) and PLX3397 twice daily (28 days of a 28 day cycle) for up to 12 cycles in the absence of progressive disease or unacceptable toxicities. After discontinuation of study drug, patients will continue to be followed for OS every 6 months. For patients participating in the run-in Phase 1b of the study, intra patient dose escalation will be permitted after a RP2D has been established. The Phase 2 portion of the study will enroll patients to be treated with PLX3397 at RP2D.~For the Phase 1b portion of the study, 2 cohorts (800 mg/day and 1000 mg/day) are planned to be enrolled at approximately 7-10 sites. Each cohort will consist of approximately 7 patients. Therefore, a minimum of 14 patients are planned to be enrolled in Phase 1b. Additional patients may be required for replacement patients, or if lower dose cohorts (600 mg or 400 mg) are required. For the Phase 2 portion of the study, enrollment is planned to include approximately 44 patients.
The study objectives are to assess the potential for PLX3397 to improve the efficacy of standard of care radiation therapy (RT) + temozolomide in patients with newly diagnosed glioblastoma (GBM).