Pomalidomide, Anti-PD-1 Antibody Combined With Selinexor (PPS) in Relapsed/Refractory Primary Central Nervous System Diffuse Large B-Cell Lymphoma

Inclusion Criteria: * Histologically confirmed primary central nervous system diffuse large B-cell lymphoma (PCNSL-DLBCL). * Disease progression or relapse after prior treatment with high-dose methotrexate and/or BTK inhibitors. * Age between 18 and 75 years. * ECOG performance status score 0-4. * Expected overall survival \> 3 months. * No known hypersensitivity to any study drug. * White blood cell count ≥ 3×10⁹/L; absolute neutrophil count ≥ 1.0×10⁹/L; platelet count ≥ 50×10⁹/L. * Serum creatinine ≤ 1.5 mg/dL; creatinine clearance ≥ 50 mL/min. * ALT and AST ≤ 3× upper limit of normal (ULN); total bilirubin ≤ 2× ULN. * Signed written informed consent. Exclusion Criteria: * Presence of another malignant tumor requiring active pharmacological or surgical intervention at present; * Female patients who are pregnant or breastfeeding; * Patients (male or female) of reproductive potential who are unwilling to use or fail to use effective contraceptive measures; * Known hypersensitivity to any study drug or any excipient ingredients of these products; * Active infection (determined by the investigator); * History of immunodeficiency, including positive HIV status, other acquired or congenital immunodeficiency disorders, or history of organ transplantation; * Documented history of neurological or psychiatric disorders, including epilepsy or dementia; * Documented history of autoimmune diseases (except Hashimoto's thyroiditis or thyroid dysfunction); * Any severe comorbidity that, in the investigator's judgment, would compromise patient safety or interfere with the completion of the study.