The main objective of this study is to evaluate the differences in objective response rate and overall survival between the Purinostat mesylate for injection and selinexor, as assessed by blinded independent central review (BICR), in patients with relapsed or refractory diffuse large B-cell lymphoma.

.The participants in the experimental group will receive treatment with Purinostat mesylate for injection. The dosage is 11.2 mg/m2. Each administration cycle consists of intravenous administration on days 1, 4, 8, and 11. A 21-day period constitutes one treatment cycle, and the total treatment cycle lasts for 6 cycles.

.Participants in the control group will receive selinexor treatment. The recommended dose is 60 mg per dose, taken orally on days 1 and 3 of each week (for example, Monday and Wednesday, or Tuesday and Thursday), and a 4-week period constitutes one treatment cycle.

Inclusion Criteria:

1. Age ≥ 18 years, no gender restrictions;
2. Histologically-confirmed DLBCL, Participants must have relapsed or failed to respond to at least two lines of prior systemic therapy (2-5 lines);
3. Participants must have measurable disease;
4. ECOG≤2;
5. Adequate organ function

Exclusion Criteria:

1. Pregnancy or breastfeeding;
2. Previous history of transplantation;
3. Double/Triple Hit B cell lymphoma;
4. Patient with known active infection, or reactivation of a latent infection;
5. Any serious diseases that investigator deems inappropriate to participate.