Inclusion Criteria  Patients must satisfy all of the following criteria to be enrolled in the study:  Histologically-confirmed diffuse large B-cell lymphoma (without central nervous system involvement) Eastern Cooperative Oncology Group performance status 0-3 Aged ≥ 80 years old or aged 70-79 with comprehensive geriatric assessment stratified as unfit or frail International normalized ratio and activated partial thromboplastin time are both 1.5 times lower than the upper limits of normal (ULN). At least 1 measurable site of disease (defined as lymph nodes with the long diameters longer than 1.5cm, or extra-nodal sites with the long diameters longer than 1.0cm; meanwhile, any lesion site with at least 2 measurable vertical diameters) Life expectancy of at least 3 months determined by researchers The patient or his or her legal representative must provide written informed consent prior to any special examination or procedure for the research. Anti-lymphoma drugs have not been used before (except glucocorticoids).  Exclusion criteria  Presence of any of the following criteria will exclude a patient from enrollment:  Uncontrolled cardio- and cerebro-vascular disease, blood clotting disorders, connective tissue diseases, serious infectious diseases and other diseases  Laboratory measures meet the following criteria at screening (unless caused by lymphoma):  Neutrophils<1.5×10^9/L Platelets<80×10^9/L (Platelets<50×10^9/L in case of bone marrow involvement) ALT or AST is 2 times higher than the upper limits of normal (ULN), AKP and bilirubin are 1.5 times higher than the ULN. Creatinine is 1.5 times higher than the ULN or eGFR is lower than 40ml/min/1.73m^2 (according to Cockcroft-Gault Equation or MDRD Equation). HIV-infected patients Left ventricular ejection fraction<50% Patients with HbsAg positive are required to have HBV DNA<1.0×10^3 IU/ml before entering the group. In addition, if the patient is HBsAg negative but HBcAb positive (regardless of HBsAb status), HBV DNA test is also required, and HBV DNA<1.0×10^3 IU/ml is required before entering the group. Other anti-tumor treatments (lymphoma or other types of tumors) are currently in progress. Patients with psychiatric disorders or patients who are known or suspected to be unable to fully comply with the study protocol Require treatment with strong/moderate CYP3A inhibitors or inducers. History of stroke or intracranial hemorrhage within 6 months prior to start of therapy Inability to swallow capsules or presence of diseases that significantly affect gastrointestinal function, such as malabsorption syndrome, post-bariatric surgery, inflammatory bowel disease and complete or incomplete intestinal obstruction Other medical conditions determined by the researchers that may affect the study