Background: Immunotherapy has become standard therapy for untreated advanced NSCLC. However, no direct comparison between anti-PD-1 inhibitors has been reported. Methods: CTONG1901 is an open label, randomized, phase II clinical trial to compare sintilimab and pembrolizumab in monotherapy or combination with chemotherapy for advanced NSCLC at first-line setting. The primary endpoint was objective response rate (ORR). Patient without EGFR and ALK alteration were enrolled. Patients with PD-L1 tumor proportion score (TPS) ≥50% were randomly to receive sintilimab (A) or pembrolizumab (B) ; and with TPS<50% were randomly to receive sintilimab (C) or pembrolizumab (D) combined with chemotherapy. Sample size was calculated by Optimal Two-Stage Designs. 20 patients were enrolled in 1^st stage. When ≥4 patients achieve partial response (PR) in sintilimab arms, the study will enter into 2^nd stage and the sample size will be calculated based on the ORR results of the 1^st stage. Results: The ORR was 57.1% in sintilimab and 33.3% in pembrolizumab arms at the 1^st stage. The study successfully entered into the 2^nd stage. 48 additional patients should be enrolled after calculation. When 15 PR in sintilimab arms achieved, the primary endpoint will be reached. From Mar. 2020 to Jan. 2022, 71 patients were screened and 68 patients were enrolled in two stages. Histologic subtypes and brain metastasis were well balanced between arms. As of Dec. 31^st 2021, the median follow-up was 5.6 months. The confirmed ORR was 45.5% (15/33) in sintilimab vs. 28.6% (10/35) in pembrolizumab arms (A vs. B: 30.8% [4/13] vs. 28.6% [4/14]; C vs. D: 55.0% [11/20] vs. 28.6% [6/21]). Unconfirmed ORR was 57.6% vs. 42.9% and disease control rate (DCR) was 87.9% vs. 91.4% in sintilimab and pembrolizumab arms. The primary endpoint was reached. Survival data was immature. Any grade and 3-4 grade treatment-related adverse events (TRAEs) were comparable in sintilimab and pembrolizumab arms (Table). Conclusions: This is the first head-to-head phase II study to directly compare two anti-PD-1 antibodies as first-line treatment in advanced NSCLC. The result suggested comparable tumor response and similar safety profile between sintilimab and pembrolizumab. Clinical trial information: NCT04252365.

SQ: squamous carcinoma; NSQ: non-squamous carcinoma; SD: stable disease.