Anti-PD-1 Antibody Combined With Pegaspargase in the Treatment of Advanced Stage NK/T-cell Lymphoma

Inclusion Criteria: * Pathologically confirmed NK/T cell lymphoma based on 2016 WHO classification * Treatment naive * Age \> 18 years * Advanced stage * Must has measurable lesion in CT or PET-CT prior to treatment * ECOG 0,1,2 * Informed consented Exclusion Criteria: * Aggressive NK/T-cell leukemia * Has accepted PD-1,PD-L1 or PD-L2 antibody before * Has accepted autologous Stem cell transplantation before * History of malignancy except for basal cell or squamous cell carcinoma of the skin or carcinoma in situ of the cervix 3 years prior to study treatment * Uncontrollable cardio-cerebral vascular, coagulative, autoimmune, serious infectious disease * Primary CNS lymphoma * Lab at enrollment (Unless caused by lymphoma): Neutrophile\<1.5\*10\^9/L ;Platelet\<50\*10\^9/L; ALT or AST \>3\*ULN; Creatinine\>2\*ULN * Other uncontrollable medical condition that may that may interfere the participation of the study * Not able to comply to the protocol for mental or other unknown reasons Pregnant or lactation * HIV infection * HBV-DNA or HCV-RNA positive * Diagnosed immunodeficiency or received systemic corticoid therapy 2 weeks prior to first dose. * Received attenuated live vaccine 4 weeks prior to first dose.