Abemaciclib Neuropharmacokinetics of Diffuse Midline Glioma Using Intratumoral Microdialysis

Background: Diffuse midline gliomas are the most aggressive brain tumors of childhood and young adults. Most people with these tumors survive less than 2 years. Researchers want to see if an anticancer drug (abemaciclib) can help. Objective: To see if researchers can measure how much abemaciclib is in a person's brain tumor and brain fluid after they take the drug for a few days. Eligibility: People aged 18 to 39 with recurrent high-grade glioma or diffuse midline glioma. Design: Participants will be screened with: Medical history Physical exam Blood and urine tests Tests of heart function Imaging scans of the brain, with a contrast agent Screening tests will be repeated during the study. Participants will also have chest X-rays. Participants will take abemaciclib by mouth twice a day for 4 and a half days. Participants will undergo surgery. They will have either a tumor biopsy (a needle will be inserted to remove a small piece of tissue) or a surgical resection (part or all of the tumor will be removed). A small tube (catheter) will be placed in their brain for 48 hours to collect fluid samples. They will have a neurological exam every few hours while the tube is in place. Two days later, the tube will be removed without surgery. Participants will stay in the hospital for about 4 days for treatment. Based on the results of abemaciclib levels in the brain, participants may keep taking abemaciclib and another drug (temozolomide) by mouth until their cancer gets worse or they have bad side effects. While taking these two drugs, participants will come back to the clinic for follow-up routinely. They will be followed by the study for life....