It's a prospective, single arm, open label phase II clinical trial, in which the safety and efficacy of Chidamide plus R-CHOP regimen is accessed in de novo DLBCL patients, who have received 2 courses of R-CHOP but only achieved PR or whose MRD tests for ctDNA revealed positive results.

abbreviation: R-CHOP: the chemo-therapy regimen composed of Rituximab, cyclophosphoamide, etoposide, vincristine and prednisone.

PR: partial remission; MRD:minimal residual disease;

Inclusion Criteria:

1. Diagnosed as diffuse large B-cell Lymphoma with positive CD20 results;
2. Age between 18 to 75 years old;
3. World health organization-Eastern Cooperative Oncology Group Performance Status (ECOG) 0-2;
4. No history of malignant tumors, having no tumor other than DLBCL at the time of enrollment;
5. Life expectancy no less than 6 months
6. The patient or his/her attorney would be able to provide written consent for necessary examinations or procedures;
7. IPI mark>1.

Exclusion Criteria:

1. History of autologous stem cell transplantation;

2. History of other malignant tumors, except skin basal cell carcinoma and in situ cervical cancer;

3. With uncontrolled cardiovascular/ cerebrovascular disease, coagulation disorders, connective tissue disease, severe infectious diseases;

4. Lymphoma originated in the central nervous system;

5. Left ventricular ejection fraction ≦50％

6. Abnormal lab results in enrollment:

   1. Neutrophil count: <1.5*109/L；
   2. Platelet count <75*109/L；
   3. AST or ALT >2 times the upper limit of normal level，AKP and total bilirubin >1.5 times the upper limit of normal level;
   4. serum creatinine >1.5 times the upper limit of normal level;

7. Other uncontrolled medical conditions which the investigators think might influence the results of the trial;

8. Patients with mental illnesses or other diseases that might not comply with the trial plan;

9. Women during pregnancy or lactation;

10. HIV positive patients;

11. HbsAg (+) patients with HBV DNA(+), can be enrolled only when his/her HBV DNA turns negative; patients with HBsAg(-) HBcAb(+) can be enrolled only when his/her HBV DNA turns negative;

All the data would be available on the corresponding website of the leading research center.