Serplulimab, a fully humanized immunoglobulin G4 (IgG4) monoclonal antibody targeting the programmed cell death protein 1 (PD-1) receptor, was approved by the National Medical Products Administration (NMPA) in January 2023 for first-line treatment of extensive-stage SCLC based on the results of the ASTRUM-005 trial. Here, PDCD1 is linked to small cell lung carcinoma.