This is a multicentre, open-label, single-arm, phase II clinical study to evaluate the safety and efficacy of sintilimab and pegaspargase in combination with pegaspargase for the initial treatment of previously untreated patients with limited stage NK/T cell lymphoma.All eligible patients will be firstly treated with sintilimab combined with pegaspargase administered every 3 weeks for 4 cycles. If the patient achieves complete remission（CR）, standard radiotherapy will be performed, otherwise, they will receive concurrent chemoradiotherapy（CCRT）(radiation 50 Gy and two cycles of sintilimab and pegaspargase every 3 weeks). After radiotherapy or CCRT, patients achieving CR with positive plasma EBV-DNA or partial response will continue with sintilimab maintenance up to 2 years.
Aim of the trial is to evaluate the safety and efficacy of sintilimab and pegaspargase in combination with pegaspargase for the initial treatment of previously untreated patients with limited stage NK/T cell lymphoma.All eligible patients will be treated with sintilimab combined with pegaspargase administered every 3 weeks for 4 cycles followed by standard radiotherapy with or without concurrent sintilimab and pegaspargase administered every 3 weeks. After radiotherapy, patients with complete remission with positive plasma EBV-DNA or partial response will continue with sintilimab maintenance up to 2 years.