Pembrolizumab, Ibrutinib and Rituximab in PCNSL

This study tests a combination of three drugs — pembrolizumab (immunotherapy), ibrutinib (a targeted drug), and rituximab (an antibody) — for patients with primary central nervous system lymphoma (PCNSL), a rare type of lymphoma that develops in the brain, whose disease has come back or did not respond to initial treatment. **You may be eligible if...** - You are 18 or older - You have been diagnosed with PCNSL that has relapsed or did not respond to prior treatment - Your disease is confirmed on brain MRI or spinal fluid tests - You are in reasonably good health (ECOG 0–1) with a life expectancy over 3 months - Your blood counts and organ function meet specific minimum levels **You may NOT be eligible if...** - You have had certain prior immunotherapy treatments - You have uncontrolled infection or active autoimmune disease - You are pregnant - You have severe organ dysfunction that prevents you from tolerating the drugs Talk to your doctor to see if this trial is right for you.