The study is about testing a new medicine called tirabrutinib for people with a type of brain cancer named Primary Central Nervous System Lymphoma (PCNSL). This cancer affects the brain and central nervous system. The study is divided into two parts: Part A is for patients whose cancer has come back or not responded to other treatments. Part B is for patients newly diagnosed with PCNSL and have not yet received any treatment.

For Part A, patients must have tried a high-dose drug called methotrexate before. For Part B, participants should be ready to start treatment with methotrexate and other cancer drugs right away.

• Part A is for those whose previous treatment didn't work; Part B is for newly diagnosed patients.
• Participants must be 18 or older and have adequate organ function.
• Risks include side effects from the drug and required medical assessments during the study.

Before joining, patients need to agree to certain tests and visits to the clinic to ensure they are suitable for the study. It's important for participants to discuss with their doctors to understand all the risks and benefits of this study.