This study is a prospective, single-arm, exploratory clinical trial designed to evaluate the efficacy and safety of IBI363 in patients with extensive-stage small cell lung cancer (ES-SCLC) who have progressed after at least two prior lines of standard therapy, including PD-1/PD-L1 inhibitor-based immunotherapy. A total of 35 patients were enrolled. The primary endpoint is the objective response rate (ORR), as assessed by investigators according to RECIST 1.1 criteria. Following a screening period of up to 28 days, patients will receive IBI363 treatment until disease progression, onset of intolerable toxicity, withdrawal of informed consent, completion of 24 months of therapy, discontinuation due to other protocol-specified reasons, or early termination of the study.