This is a phase II, open-label, non-randomized, single-arm, multicenter study to evaluate the efficacy, safety, and PK of chidamide in patients with R/R PTCL.

This is a phase II, open-label, non-randomized, single-arm, multicenter study to evaluate the efficacy, safety, and PK of chidamide in patients with R/R PTCL. To determine eligibility, subjects must have PTCL confirmed with a sample or specimen evaluated by the investigator.A treatment cycle is defined as 4 weeks. All eligible subjects will be treated with chidamide until disease progression, intolerable toxicity effects, death, or withdrawal of consent.

Inclusion Criteria:

1. Histopathological diagnosis, made by the investigator, of the following PTCL subtypes as defined by the WHO classification (2016) may be included: PTCL, not otherwise specified (PTCL-NOS), anaplastic lymphoma kinase-positive (ALK+) anaplastic large-cell lymphoma (ALCL), ALK-negative (ALK-) ALCL, angioimmunoblastic T-cell lymphoma (AITL), extranodal natural killer (NK)/T-cell lymphoma, nasal type (ENKL), etc., except cutaneous form or leukemic form.
2. Patients for whom at least one measurable lesion according to Cheson Criteria 2014 at baseline.
3. Relapsed or refractory disease (including DOR shorter than 30 days) to ≥1 prior systemic therapy including, but not limited to, chemotherapy, target therapy, immunotherapy, and autologous stem cell transplantation.
4. Male or female, aged 20-75 years (inclusive).
5. Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1.
6. With a life expectancy of ≥12 weeks.
7. Have not received radiotherapy, chemotherapy, immunotherapy (except for antibody therapy), or target therapy within 4 weeks prior to the start of study drug.
8. Have not received any antibody therapy within 12 weeks prior to the start of study drug.
9. Willing to provide written informed consent.

Exclusion Criteria:

1. Females who are pregnant or breastfeeding, or females of childbearing potential who are not willing to use adequate contraception.
2. Patients in whom central nervous system lymphoma is recognized during screening (if suspected clinically, imaging study should be performed to confirm).
3. Have been treated with histone deacetylase (HDAC) inhibitor.
4. With a history of clinically significant QTc prolongation (>450 ms for males or >470 ms for females), ventricular tachycardia (VT), atrial fibrillation (AF), heart block (HB), myocardial infarction (MI) onset within one year, congestive heart failure (CHF), or any other symptomatic coronary artery disease requiring treatment.
5. The size of fluid area detected by cardiac ultrasonography in cavum pericardium is ≥10 mm during diastolic period.
6. With a history of organ transplantation.
7. With a history of allogeneic stem cell transplantation.
8. Have received autologous stem cell transplantation within 12 weeks prior to the start of study drug.
9. Have participated in a clinical trial involving investigational antibody therapy within 12 weeks prior to the start of study drug or non-antibody therapy within 4 weeks prior to the start of study drug.
10. Have received symptomatic treatment for early myelotoxicity within 7 days prior to the start of study drug.
11. With active bleeding or newly diagnosed thromboembolic disease, or with hemorrhagic tendency who are using anticoagulants.
12. With active infection of hepatitis B or C, or persistent fever within 14 days prior to the start of study drug.
13. With history of testing positive for human immunodeficiency virus or known acquired immunodeficiency syndrome.
14. Had a major organ surgery within 6 weeks prior to the start of study drug.
15. With abnormal hepatic function (serum total bilirubin >1.5 x upper limit of normal [ULN]; alanine aminotransferase [ALT]/aspartate aminotransferase [AST] >2.5 x ULN or >5 x ULN if liver metastases are present), abnormal renal function (serum creatinine >1.5 x ULN), or abnormal complete blood count (absolute neutrophil counts <1500/μL; platelet counts <90 x 1000/μL, hemoglobin <9 g/dL).
16. Has known psychiatric disorders or substance abuse disorders that may interfere with the patient's participation in the study or evaluation of the study results.
17. Considered by the investigator as being not suitable to participate the study.