Maintenance Treatment of Chidamide in Stage IV or Relapsed/Refractory Extranodal NK/T-cell Lymphoma

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.