Small cell lung cancer (SCLC) is highly malignant and aggressive, with most patients presenting with metastases at diagnosis. For postoperatively incidentally detected SCLC (identified unexpectedly in pathological examinations after surgery), conventional adjuvant chemoradiotherapy has shown limited efficacy, characterized by high recurrence rates and suboptimal long-term survival.Notably, advances in immunotherapy have transformed SCLC management. The EXTENTORCH trial, a pivotal study published in JAMA Oncology, demonstrated that toripalimab plus chemotherapy significantly improved outcomes in extensive-stage SCLC (ES-SCLC), achieving a reduced risk of progression or death (HR=0.67, 95% CI 0.54-0.82, P\<0.001) with manageable safety, marking a substantial therapeutic breakthrough. Given the proven efficacy of toripalimab in ES-SCLC, there is a strong rationale to extend this strategy to postoperatively incidentally detected SCLC. This trial aims to evaluate the efficacy and safety of toripalimab as adjuvant maintenance therapy in this cohort, with the objective of reducing recurrence and enhancing long-term survival.