A Multicenter, Prospective Clinical Trial With a Concurrent Control Evaluating Methotrexate Combined With Rituximab,Sintilimab and Pirtobrutinib vs. Investigator-Selected Standard of Care in Treatment-Naive PCNSL

Inclusion Criteria: 1. Age \>= 18 years. 2. Voluntarily signed informed consent. 3. ECOG Performance Status 0-3. 4. Expected survival \> 3 months. 5. Histopathologically confirmed Diffuse Large B-Cell Lymphoma (DLBCL) restricted to the CNS or eyes (PCNSL). 6. Measurable lesion on contrast-enhanced MRI (\>10x10 mm) or positive CSF cytology for leptomeningeal disease. 7. No prior systemic treatment for lymphoma (corticosteroids excepted). 8. Adequate bone marrow and organ function (ANC \>=1.5x10\^9/L, PLT \>=80x10\^9/L, Hb \>=80 g/L; Bilirubin \<=1.5xULN, AST/ALT \<=2.5xULN; Creatinine \<=1.5xULN or CrCl \>=60 mL/min) . 9. Stable controlled comorbidities allowed (e.g., hypertension with blood pressure \<=160/100 mmHg, type 2 diabetes with HbA1c \<=8%, mild coronary heart disease without myocardial infarction in the past 6 months). 10. Basic communication ability to complete PROs questionnaires (no severe cognitive impairment). 11. Reproductive-aged females and males with childbearing potential: No pregnancy plans during the study and 3 months after treatment discontinuation; use effective contraception (abstinence, physical contraception, or hormonal contraceptives initiated \>=3 months before first dose). Males prohibited from donating sperm during treatment and 3 months after discontinuation. 12. For Observational Cohort (Palliative Care Subgroup only): Pathologically confirmed DLBCL restricted to the CNS or eyes; Follow-up available for efficacy assessment (at least one CR evaluation) . Exclusion Criteria: 1.Prior treatment with PD-1/PD-L1 inhibitors or CTLA4 monoclonal antibodies. Uncontrolled active infection. 2.Uncontrolled or significant cardiovascular diseases: 3.Congestive heart failure (NYHA class III/IV), 1. myocardial infarction, unstable angina within 6 months before first dose; arrhythmia requiring treatment; LVEF \<50%. 2. Primary cardiomyopathy. 3. History of clinically significant QTc prolongation, second-degree type II/third-degree atrioventricular block, or QTc interval (Fridericia method) \>470 msec (females) / \>480 msec (males). 4. Atrial fibrillation (EHRA grade ≥2b). 5. Refractory hypertension. 4.Active hepatitis B/C infection (HBV-DNA ≥ detection limit, HCV RNA positive) or syphilis. (Exceptions: HBV-DNA \< detection limit, cured HCV). 5.HIV infection. 6.Prior organ transplantation or allogeneic stem cell transplantation. 7.Pregnant or lactating females. 8.Prior/current pulmonary fibrosis, interstitial pneumonia, pneumoconiosis, or radiation pneumonitis (unsuitable for study per investigator). 9.Autoimmune diseases requiring systemic treatment within 2 years. 10.For Observational Cohort (Palliative Care Subgroup only): Incomplete clinical data (e.g., no pathological report, inability to perform MRI/PET-CT assessment).