Peposertib and Radiation Therapy, Followed by Temozolomide for the Treatment of Patients With Newly Diagnosed MGMT Unmethylated Glioblastoma or Gliosarcoma

This study tests a drug called peposertib combined with radiation therapy, followed by a chemotherapy drug (temozolomide), for patients newly diagnosed with glioblastoma — the most aggressive form of brain cancer — in cases where the tumor lacks a specific repair gene (MGMT unmethylated). **You may be eligible if...** - You are 18 or older - You have been newly diagnosed with glioblastoma (grade 4 brain tumor) or gliosarcoma confirmed by biopsy - You have not received prior treatment for this brain tumor - You are in reasonably good functional health - Your organs are functioning adequately - You have had a recent brain MRI (within 14 days of starting) **You may NOT be eligible if...** - Your tumor has IDH mutations (a different subtype of brain tumor) - You have severe organ dysfunction unrelated to your brain tumor - You are pregnant or breastfeeding - You cannot tolerate radiation therapy Talk to your doctor to see if this trial is right for you.