Pembrolizumab + Chemotherapy in Newly Diagnosed PCNSL

This study is testing a combination of pembrolizumab (immunotherapy) and chemotherapy as initial treatment for primary central nervous system (CNS) lymphoma — a type of lymphoma (blood cancer) that starts in the brain or spinal cord. Currently, treatment options are limited, and researchers want to see if adding immunotherapy to existing chemotherapy improves outcomes. **You may be eligible if...** - You are 18 years old or older - You have been newly diagnosed with primary CNS diffuse large B-cell lymphoma (confirmed by brain biopsy, spinal fluid, or eye fluid) - You have not yet received any chemotherapy or whole-brain radiation for this diagnosis - You are generally functional (not severely debilitated) - Your blood counts, kidney, and liver functions are adequate **You may NOT be eligible if...** - You cannot undergo MRI scans - You have active autoimmune disease requiring immune-suppressing treatment - You have previously received immunotherapy drugs targeting PD-1 or PD-L1 - You have HIV or a history of organ transplant - You have active or poorly controlled diabetes (HbA1c > 8%) - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.