Background: NK/T-cell lymphoma (NKTL) is a rare and distinct subtype NHL. Most newly diagnosed NKTL cases were localized-stage. For localized NKTL, RT alone is inadequate due to high systemic failure rate. Chemoradiation has been increasingly applied. However, current chemotherapy (CT) regimens have severe toxicity and infection, which reduce the completion of RT and patients’ medical compliance. Therefore, novel regimens with mild toxicity are needed. Sintilimab, a fully human anti-PD-1 monoclonal antibody, has showed encouraging antitumor efficacy in pts with r/r NKTL. Anlotinib, a multiple-targeted TKI that mainly blocks VEGF/VEGFR pathway, has been approved for several solid tumor types in china. Anti-angiogenesis therapy could improve efficacy of ICI in multiple tumor types. This multicenter, single-arm, phase 2 study aims to evaluate the efficacy and safety of sandwich chemoradiotion of sintilimab combined with anlotinib and pegaspargase (PEG-ASP) in newly diagnosed localized NKTL pts. Methods: Patients with pathologically confirmed previously untreated stage NKTL were enrolled. All enrolled patients received 3 cycles of sintilimab (200mg D1 ivdrip) combined with anlotinib (12mg po D1-14) and PEG-ASP (2500U/m² D1) every 3 weeks followed by RT, then received additional 3 cycles of combination therapy as described above. The primary endpoint was overall response rate (ORR) by LUGANO 2014 criteria. Results: A total of 39 pts were enrolled, and 24 pts eligible for response evaluation (70.8% men; median age, 46 y [range 20-64]; 58.3% stage). According to PINK-E system, 8 pts (33.3%) were identified as intermediate risk group and 16 patients were low risk group. 23 of 24 patients completed protocol-specified therapeutic schemes, one patient discontinued the study after the second cycle due to disease progression. ORR was 95.8% (23/24, 95%CI: 76.9%-84.1%). Surprisingly, all the responded patients achieved CR, while 66.7% (16/24, 95%CI: 44.7%-83.6%) patients achieved CR after the second cycle. Median PFS and OS have not been reached. 1-year OS and PFS was 100% and 95.8%, respectively. All grade TRAEs occurred in 84.6% of all enrolled patients and 92.1% were grade 1-2. The most common TRAE was lymphocytopenia (9.9%). Of note, grade 3-4 hematological toxicity was reported in only one patient (4.2%). All AEs were resolved after symptomatic treatment, without systematic corticosteroid intervention. Conclusions: Sintilimab combined with anlotinib and PEG-ASP upfront and after radiotherapy was effective and could be well tolerated in localized NKTL, achieving promising CRR and rapid and long-term remission with mild toxicity. Further investigation of survival outcome is warranted. Clinical trial information: NCT03936452