Serplulimab, a novel anti-PD-1 antibody, plus chemotherapy versus chemotherapy alone as first-line treatment for extensive-stage small-cell lung cancer: An international randomized phase 3 study.

8505 Background: Monoclonal antibodies against programmed death-ligand 1 (PD-L1) have been approved for the first-line treatment of extensive-stage small-cell lung cancer (ES-SCLC) in combination with chemotherapy. However, whether a programmed death 1 (PD-1) inhibitor provides similar survival benefit in this patient population remains unclear. In this study, the efficacy and safety of serplulimab, a novel humanized monoclonal anti-PD-1 antibody, were assessed in combination with chemotherapy in previously untreated ES-SCLC patients. Methods: In this international, randomized, double-blind, multicenter, phase 3 trial (NCT04063163), patients with ES-SCLC who had not received prior systemic therapy were randomized (2:1) to receive serplulimab 4.5 mg/kg or placebo intravenously every 3 weeks. All patients received intravenous carboplatin and etoposide every 3 weeks for up to 4 cycles. The primary endpoint was overall survival (OS). Secondary endpoints included progression-free survival (PFS), objective response rate (ORR), duration of response (DoR), and safety. Results: Between September 12, 2019 and April 27, 2021, 585 patients were randomized (serplulimab group, n = 389; placebo group, n = 196). At interim analysis, the median follow-up duration was 12.3 months. Median OS was significantly prolonged in the serplulimab group than the placebo group (15.4 vs.10.9 months; hazard ratio [HR] 0.63, 95% CI 0.49–0.82; P < 0.001). Median PFS assessed by the independent radiology review committee (IRRC) per RECIST v1.1 was significantly longer in the serplulimab group than the placebo group (5.8 vs. 4.3 months; HR 0.47, 95% CI 0.38–0.59; P < 0.001). Efficacy improvements were also observed in ORR (80.2% vs. 70.4%) and DoR (5.6 vs. 3.2 months) as assessed by IRRC per RECIST v1.1. Grade ≥3 treatment-emergent adverse events (TEAEs) related to serplulimab or placebo were reported in 129 (33.2%) and 54 (27.6%) patients in the respective groups. Incidence of immune-related TEAEs was higher in the serplulimab group compared to the placebo group (37% vs. 18.4%), with the largest difference in endocrine disorders (18.3% vs. 4.6%), which are commonly reported with anti-PD-1/PD-L1 therapies. Four deaths (1 acute coronary syndrome, 1 pyrexia, and 1 platelet count decreased in the serplulimab group; 1 thrombocytopenia in the placebo group) that might be related to study drugs were reported. Conclusions: Serplulimab plus chemotherapy as first-line treatment provided significant benefits and a manageable safety profile compared with chemotherapy alone in ES-SCLC patients. For the first time, OS benefits was demonstrated with a PD-1 inhibitor in a global phase 3 study among previously untreated ES-SCLC patients. Clinical trial information: NCT04063163.