Study of Pomalidomide Combination with Rituximab and Anti-PD-1 Antibody （PPR） in Third or Later Line Therapy of DLBCL

Inclusion Criteria: * Patients voluntarily joined the study, signed the informed consent, and had good compliance; * Patients with 18 Years to 80 Years(at the time of signing the informed consent); Eastern Cooperative Oncology Group Performance Status (ECOG-PS) score: 0-2; * Patients with histopathologically confirmed diffuse large B-cell lymphoma with evaluable lesions who did not achieve CR or relapsed after second-line therapy * Female patients of reproductive age should agree that birth control (such as intrauterine device, birth control pills, or condoms) must be used during the study period and for six months after completion; Having a negative serum pregnancy test within 7 days prior to study enrollment, and must be non-lactating; Male patients should agree to use contraception during the study period and for six months after the end of the study. Exclusion Criteria: * Pathological subtypes: primary central nervous system DLBCL or primary mediastinal large B-cell lymphoma. * Presence of severe or uncontrolled comorbid conditions including, but not limited to, symptomatic congestive heart failure, uncontrolled hypertension, unstable angina, active peptic ulcer disease, or severe hemorrhagic disorders such as hemophilia A, hemophilia B, von Willebrand disease, or history of spontaneous bleeding requiring transfusion or other medical interventions. * A history of any active immune or autoimmune disease, or a known history of allogeneic organ transplantation or allogeneic hematopoietic stem cell transplantation; * Any active infection requiring systemic antimicrobial therapy within 14 days before starting study treatment, including, but not limited to, bacterial, fungal, and viral infections. * Current participation in other clinical studies, or initiation of study drugs administration less than 4 weeks after completion of previous clinical study treatment. * Patients with concomitant diseases that, in the investigator's judgment, may seriously endanger patients' safety or may interfere with the completion of the study, or are deemed unsuitable for inclusion for other reasons.