Sintilimab, Pegaspargase and Anlotinib for Stage IV Natural Killer /T-cell Lymphoma

Inclusion Criteria: * Histopathology and immunohistochemistry confirmed diagnosis of NK/T-cell lymphoma according to WHO 2016 criteria. * Stage IV disease according Lugano 2014 staging system. Newly diagnosed patients, or relapsed disease without a history of asparaginase-containing regimen. * PET/CT or CT/MRI with at least one objectively evaluable lesion. * The age is greater than 65 years old. Those who are younger than 65 years should have a documented history unfit for high-dose combination chemotherapy (ie. high doses of methotrexate or high doses of dexamethasone, or autologous hematopoietic stem cell transplantation). * General status ECOG score 0-3 points. * The laboratory test within 1 week before enrollment meets the following conditions: Blood routine: Hb\>80g/L, PLT\>50×109/L. Liver function: ALT, AST, TBIL ≤ 2 times the upper limit of normal. Renal function: Cr is normal. Coagulation : plasma fibrinogen ≥ 1.0g / L. Cardiac function: LVEF≥50%, ECG does not suggest any acute myocardial infarction, arrhythmia or atrioventricular conduction above I Blocking. * Sign the informed consent form. * Voluntary compliance with research protocols, follow-up plans, laboratory and auxiliary examinations. Exclusion Criteria: * Patients with a history of pancreatitis. * Active infection requires ICU treatment. * Concomitant HCV or HIV infection. Patients who are infected with HBV at the same time are not excluded. * Serious complications such as fulminant DIC. * Significant organ dysfunction: such as respiratory failure, NYHA classification ≥ 2 chronic congestive heart failure, decompensation Hepatic or renal insufficiency, high blood pressure and diabetes that cannot be controlled despite active treatment, and cerebral vascular thrombosis or hemorrhagic time within the past 6 months. * Pregnant and lactating women. * Had a history of autoimmune diseases, and disease was active in the last 6 months, and was still taking oral immunosuppression in the past three months. For the treatment, the daily dose of oral prednisone is greater than 10 mg. * Those who were known to be allergic to drugs in the study regimen. * Patients with other tumors who require surgery or chemotherapy within 6 months. * Other experimental drugs are being used.