To evaluate the efficacy and safety of chidamide monotherapy as maintenance treatment in patients with diffuse large B-cell lymphoma (DLBCL) and HBV infection following initial response to R-CHOP therapy, and to provide evidence for the clinical application of chidamide.

Primary endpoint is 2-year progression-free survival (PFS). Secondary endpoints include overall survival (OS), safety parameters, and exploratory biomarkers.

Inclusion Criteria:

1. Both sexes, age range ≥18 years and ≤80 years.
2. No prior treatment for DLBCL, including chemotherapy, targeted therapy, immunotherapy, local radiotherapy for lymphoma (except local radiotherapy used to relieve tumor-related symptoms), or surgical treatment (except for tumor or pathological tissue biopsy and surgical resection not targeting lymphoma). Patients must have achieved complete response (CR) after 6 cycles of R-CHOP chemotherapy, confirmed by imaging (CT/PET-CT), bone marrow biopsy (if positive at baseline), and clinical assessment. Eligible patients will be randomly assigned in a 1:1 ratio to either the chidamide maintenance treatment group (experimental group) or the observation group (control group).
3. Histopathologically confirmed diagnosis (all of the following conditions must be met simultaneously): Diffuse large B-cell lymphoma (DLBCL), and CD20-positive; Positive result for hepatitis B infection, defined as HBsAg positive, HBV DNA positive (>2000 IU/mL), or histopathological evidence of chronic HBV infection (without cirrhosis). Patients receiving ongoing antiviral therapy (e.g., nucleos(t)ide analogs) must have been on a stable regimen for ≥4 weeks prior to enrollment.
4. Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2.
5. At screening, laboratory tests must meet the following criteria, unless judged by the investigator to be due to lymphoma (no corrective or supportive treatment for the parameters below within 2 weeks prior to assessment): Hematology: Hemoglobin (Hb) ≥ 90 g/L, Absolute neutrophil count (ANC) ≥ 1.5 × 10⁹/L, Platelet count (PLT) ≥ 90 × 10⁹/L; Biochemistry: Serum creatinine (Cr) ≤ 1.5 × upper limit of normal (ULN); Total bilirubin (TBIL) ≤ 1.5 × ULN; Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 2.5 × ULN (≤ 5 × ULN in cases of liver metastasis).
6. Life expectancy of at least 6 months, as judged by the investigator.
7. Understand and voluntarily sign a written informed consent form.

Exclusion Criteria:

1. Pregnant or breastfeeding women, and fertile patients unwilling to use contraceptive measures.
2. Patients with a history of clinically significant QTc interval prolongation (males > 450 ms, females > 470 ms), ventricular tachycardia (VT), atrial fibrillation (AF), heart block, myocardial infarction (MI) within 1 year, congestive heart failure (CHF), or symptomatic coronary artery disease requiring medication.
3. Patients who have undergone organ transplantation.
4. Patients who received treatment for prior myelotoxicity as symptomatic therapy within 7 days before enrollment.
5. Patients with active bleeding.
6. Patients with a history or current diagnosis of thrombosis, embolism, cerebral hemorrhage, cerebral infarction, or other related conditions.
7. Patients with active infection, or persistent fever within 14 days before enrollment.
8. Patients who have not completed at least 6 weeks of recovery after major organ surgery.
9. Patients with abnormal liver function (total bilirubin > 1.5 × upper limit of normal [ULN], ALT/AST > 2.5 × ULN, or > 5 × ULN in patients with liver involvement) or abnormal renal function (serum creatinine > 1.5 × ULN).
10. Patients with mental disorders or those from whom informed consent cannot be obtained.
11. Patients with drug abuse or chronic alcoholism that may interfere with the evaluation of trial results.
12. Patients with lymphoma involving the central nervous system (CNS).
13. Patients deemed by the investigator to be unsuitable for participation in this study.