Chidamide Maintenance for MRD-Positive Double-Expressor DLBCL in First Complete Remission

Inclusion Criteria: * Histologically confirmed diffuse large B-cell lymphoma, CD20-positive. * Double-expressor lymphoma confirmed by pathology, defined as MYC expression \>=40% and BCL2 expression \>=50% by immunohistochemistry. * Complete response after initial induction therapy. * Age \>=18 and \<=80 years. * ECOG performance status 0-2. * No prior history of malignant tumor and no concurrent malignancy. * International Prognostic Index (IPI) score \>1. * ctDNA MRD-positive at screening/enrollment. * Life expectancy of at least 6 months, in the opinion of the investigator. * Written informed consent provided before any study-specific procedure. Exclusion Criteria: * Failure to achieve complete response after initial induction therapy. * Prior organ transplantation. * Uncontrolled coagulopathy or active bleeding. * Uncontrolled cardiovascular or cerebrovascular disease, including left ventricular ejection fraction \<50%, connective tissue disease, or severe active infection. * Major organ surgery within 6 weeks before screening. * Screening laboratory abnormalities not attributable to lymphoma, including: neutrophil count \<1.5 x 10\^9/L; platelet count \<80 x 10\^9/L (or \<50 x 10\^9/L in patients with bone marrow involvement); total bilirubin \>1.5 x upper limit of normal; ALT/AST \>2.5 x upper limit of normal, or \>5 x upper limit of normal in patients with hepatic involvement; serum creatinine \>1.5 x upper limit of normal. * Active hepatitis B not meeting protocol-defined virologic criteria for enrollment; patients with positive HBsAg or positive HBcAb require HBV DNA testing and must meet protocol-specified thresholds. * HIV infection. * Ongoing antitumor therapy for lymphoma or another malignancy. * Drug abuse or chronic alcohol abuse that may interfere with study evaluation. * Psychiatric illness or any condition resulting in inability to comply with the protocol. * Requirement for ongoing treatment with strong or moderate CYP3A inhibitors or inducers; patients exposed to these agents within 7 days before first study dose, or within fewer than 5 half-lives, are not eligible. * Inability to swallow capsules or clinically significant gastrointestinal disorders that may affect drug absorption, including malabsorption syndrome, bariatric surgery, inflammatory bowel disease, or partial/complete bowel obstruction. * Any other uncontrolled medical condition that, in the investigator's judgment, may compromise safety, interfere with oral drug absorption or metabolism, or place the participant at excessive risk.