Dexamethasone, Azacytidine,Pegaspargase and Tislelizumab for NK/T Cell Lymphoma

Inclusion Criteria: * age 18-70 years ,Eastern Cooperative Oncology Group (ECOG) performance status of 0-2 * patients with confirmed pathological diagnosis of ENKTL as defined by WHO criteria * at least one measurable lesion * hemoglobin ≥90 g/l, absolute neutrophil count ≥ 1.5 × 10\^9/L, platelets ≥ 75 ×10\^9/L), ALT≤ 2 times upper limit of normal, serum creatinine ≤1.5 times upper limit of normal （If the above indicators are abnormal but are caused by the primary disease as assessed by the clinician, the treatment can be enrolled according to the clinical actual situation） * There was no other serious disease in conflict with this program * Adequate respiratory function * Adequate bone marrow function * Adequate renal and hepatic function * Not pregnant or nursing ,negative pregnancy test * No other active malignancy requiring therapy * No other serious or life-threatening condition deemed unacceptable by the principal investigator * Life expectancy ≥ 3 months * Able to understand and sign an informed consent form (ICF). Exclusion Criteria: * NK/T cell lymphoma without confirmed pathological diagnosis; * Patients with early stage upper aerodigestive tract NK/T- cell lymphoma ; * Patients with drug allergies or metabolic disorders in the program; * Any uncontrolled medical diseases (including uncontrolled diabetes, severe heart, lung, liver and kidney dysfunction); * Severe infection (excluding the following: HBsAg or anti-HBc positive patients taking entecavir, tenofovir and other drugs;HCV RNA positive but taking direct anti-HCV drugs); * Invasion of primary or secondary central nervous system tumor invasion; * Contradictions to chemotherapy or radiotherapy; * Previously other malignancy requiring therapy; * Peripheral nervous system disorder or mental disorder; * Incapacity for legal conduct, medical or ethical reasons that affect the continuation of the research; * Other clinical investigators; * Combination of anti-tumor drugs outside the research program; * Participants evaluated inappropriate to participate in this study by principal investigator.