Lung cancer remains a leading cause of cancer-related deaths worldwide, with small cell lung cancer (SCLC) accounting for 15-20% of all lung cancers. Extensive-stage SCLC (ES-SCLC) is associated with poor prognosis, with a median survival of 2-4 months without treatment. Although platinum-based chemotherapy is the standard first-line treatment, median survival remains under one year, highlighting the need for improved outcomes. Recent studies have demonstrated that combining PD-1 inhibitors with chemotherapy can significantly improve survival in ES-SCLC patients. Serplulimab, a novel PD-1 inhibitor, has shown promising results in extending overall survival when combined with chemotherapy in a Phase III trial. Additionally, aspirin has been found to enhance the anti-tumor effects of immunotherapy by inhibiting immune checkpoint proteins and reducing adverse events such as thrombosis and fever. This Phase II study aims to evaluate the efficacy and safety of combining serplulimab, platinum-based chemotherapy, and aspirin as a first-line treatment for patients with ES-SCLC.