The Efficacy and Safety of Chidamide, Anti-PD-1 Antibody in Combination With Pegaspargase Versus DDGP in the Treatment of Newly Diagnosed, Stage III to IV Extranodal Natural Killer/T-Cell Lymphoma

Inclusion Criteria: * Confirmed histological diagnosis of NKTCL * No previous anti-lymphoma treatment * Age 14-70 years * Ann Arbor stage III-IV * At least one measurable/evaluable site after diagnostic biopsy before treatment start * ECOG performance status of 0-2 * Adequate hematological and organ function; i.e. ANC \>1000 cells /mmc, platelet counts \> 50.000/mmc, Hemoglobin \> 8 g/dl AST, ALT \> 1.5 x ULN; serum bilirubin \> 2x ULN (patient with Gilbert disease can be enrolled), Serum creatinine \> 2 x ULN or creatinine clearance \> 50ml/min * Tumor tissue (fresh preferred, achievable tissue is also acceptable) * For women of childbearing potential a negative pregnancy test on day 1 of cycle 1 and agree to adopt adequate measure to avoid pregnancy during study treatment and for at least one year from EOT. * For men agreement to remain abstinent or to use barrier contraception * Signed Informed consent Exclusion Criteria: * Confirmed histological diagnosis of aggressive NK cell leukemia * Early stage disease (AA stage I-II) * Evidence of suspect of CNS disease. * Has an active autoimmune disease that has required systemic treatment in past 2-years (ie, with use of disease modifying agents, corticosteroids or immunosuppressive drugs), including but not limited to myasthenia gravis, myositis, autoimmune hepatitis, systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease, vascular thrombosis associate with antiphospholipid syndrom…