This is a single-arm, open-lable exploratory study of Lurbinectedin in combination with Serplulimab as maintenance therapy in participants with extensive-stage small-cell lung cancer (ES-SCLC) after first-line induction therapy with carboplatin, etoposide, and Serplulimab. The study consists of 2 phases: an induction phase and a maintenance phase. Participants need to have an ongoing response or stable disease per the Response Evaluation Criteria in Solid Tumor (RECIST) v1.1 criteria after completion of 4 cycles of carboplatin, etoposide, and Serplulimab induction treatment in order to be considered for eligibility screening for the maintenance phase. Eligible participants will receive lurbinectedin plus Serplulimab in the maintenance phase.