Paxalisib (GDC-0084) In Recurrent Or Refractory PCNSL

This study tests a drug called paxalisib (GDC-0084) in people with primary central nervous system lymphoma (PCNSL) — a type of lymphoma that occurs in the brain — that has come back or stopped responding to treatment. **You may be eligible if...** - You are 18 or older - You have confirmed primary large B-cell lymphoma of the brain (PCNSL) that has returned or did not respond to prior treatment - You have measurable disease on a brain MRI - You have a Karnofsky Performance Status of 70 or higher (able to care for yourself) - You have recovered from side effects of prior treatments **You may NOT be eligible if...** - You require high-dose steroids (more than 8 mg dexamethasone per day) that cannot be reduced - You have active serious infections or uncontrolled diabetes - Your bone marrow, liver, or kidney function is too poor - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.