Efficacy and Safety of Polatuzumab Vedotin, Rituximab Combined With Reduced-dose Cyclophosphamide, Doxorubicin and Prednisone Regimen in the Treatment of Elderly Patients With Diffuse Large B-cell Lymphoma: A Multicenter, Single-arm, Prospective Study

Inclusion Criteria: 1. Histologically confirmed diagnosis of diffuse large B-cell lymphoma (DLBCL). 2. Age \>= 75 years; or age \>= 65 years with a G8 screening score \<= 14. 3. Assessed as "frail / poor tolerance" by geriatric assessment during screening, defined as meeting any one of the following: (a) G8 score \<= 14; (b) IADL score \<= 7; (c) \>= 5 cumulative Grade 2 comorbidities on CIRS-G; (d) \>= 1 system with a Grade 3-4 comorbidity on CIRS-G. 4. No prior systemic anti-tumor therapy for DLBCL, including chemotherapy, immunotherapy, targeted therapy or radiotherapy. 5. Adequate major organ function, defined as: (a) Hematologic: absolute neutrophil count (ANC) \>= 1.0 x 10\^9/L, platelets (PLT) \>= 75 x 10\^9/L; (b) Hepatic: AST and ALT \<= 3 x upper limit of normal (ULN), total bilirubin \<= 1.5 x ULN; (c) Renal: creatinine clearance (Ccr) \>= 30 mL/min; (d) Cardiac: left ventricular ejection fraction (LVEF) within the institutional normal range by echocardiography, or LVEF \>= 50%. 6. Expected survival \>= 3 months. 7. The patient or their legal representative voluntarily participates in the study and signs the written informed consent form. Exclusion Criteria: 1. Prior anti-tumor therapy directed at DLBCL. 2. Bone marrow involvement or involvement of immune-privileged sites. 3. Concurrent other active malignancy, or a prior malignancy that in the investigator's judgment may affect the efficacy and safety evaluation of this study. 4. Currently participating in another interventional clinical study, or receiving other anti-tumor drug therapy that may affect the efficacy assessment of this study. 5. Uncontrolled active infection. 6. Severe cardiac, pulmonary, hepatic, renal or other major organ dysfunction that in the investigator's judgment precludes tolerance of the study treatment. 7. Other conditions considered unsuitable for enrollment by the investigator. 8. Patients eligible for transplantation.