Extranodal natural killer/T-cell lymphoma, nasal type (NKTCL) is a highly aggressive peripheral T-cell lymphoma (PTCL). Patients with newly diagnosed stage IV and relapsed/refractory have poor prognosis. 5-year progression-free survival was reported only 55%. Chidamide is a selective histone deacetylase inhibitor which was approved by FDA in treating relapsed or refractory PTCL. In phase I and II studies of chidamide, patients with relapsed or refractory NKTCL achieved a higher overall remission. Patients who obtained complete or partial remission had much favourable duration of remission. Thus, the invesgator design this study to evaluate the role of maintenance treatment of chidamide for induction chemotherapy-responded newly-diagnosed advanced and relapsed/refractory NKTCL patients.

Inclusion Criteria:

1. diagnosis of NKTCL with typical morphology and immunophenotype, according to the 2008 World Health Organization classification of lymphomas;
2. newly-diagnosed stage IV disease or relapsed or refractory disease；
3. age ≥ 18 years;
4. ECOG performance status 0-2;
5. at least one measurable lesion;
6. adequate hematological, hepatic, and renal functions; e.g., absolute neutrophil count ≥ 1.5 × 109/L, platelet count ≥ 80 × 109/L, total bilirubin ≤ 1.5 × upper limit of normal, alanine transaminase and aspartate transaminase ≤ 2 × upper limit of normal, and creatinine ≤ 1.5 mg/dl;
7. life expectancy of more than 3 months.

Exclusion Criteria:

1. Patients with newly-diagnosed stage I-II disease;
2. pregnancy or lactation;
3. any coexisting medical problems of sufficient severity to prevent full compliance with the study protocol.