Small cell lung cancer (SCLC) is one of the most aggressive lung cancer subtypes, accounting for approximately 15-20% of total lung cancer cases. Although SCLC is relatively sensitive to chemotherapy, it is highly susceptible to recurrence. The advent of immunotherapy has revolutionized the clinical practice of oncology, and the newly released results of the ASTRUM-005 study have led to the incorporation of Serplulimab into the first-line treatment of extensive-stage SCLC. Although immunotherapy in combination with chemotherapy is currently the most promising regimen, due to the limited understanding of genetic alterations and the marked genetic heterogeneity of SCLC, treatment responsiveness varies greatly. Thus, there is an urgent need to find molecular biomarkers that can effectively predict prognosis and further suggest the effectiveness of this new treatment mode.

Minimal residual disease (MRD) refers to the presence of tumor cells disseminated from the primary lesion to distant organs in patients who lack any clinical or radiological signs of metastasis or residual tumor cells left behind after local therapy that eventually lead to local recurrence. These years, the development of real-time, high-sensitivity liquid biopsy assays have enabled the identification of MRD in individual patients with cancer. Multiple studies have demonstrated that detection of MRD dynamics following definitive therapy for solid cancers is strongly prognostic and has extremely high positive predictive value for risk of recurrence and treatment efficacy.

The aim of this study was to explore the predictive value of MRD dynamics on disease prognosis before and after the first-line treatment of Serplulimab in combination with chemotherapy for extensive-stage SCLC.

Key Inclusion Criteria:

• Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 2.
• Have previously untreated and confirmed by histological and imaging examinations as extensive small cell lung cancer
• Adequate organ function and expected survival time ≥ 12 weeks;
• Evidence of post-menopausal status or negative urinary or serum pregnancy test for female pre-menopausal patients.

Key Exclusion Criteria:

• Presence of mixed carcinoma component on histology.
• Patients with other active malignancies within 5 years prior to enrollment.
• Known active autoimmune diseases.
• Currently participate in an interventional clinical study treatment or have been treated with another drug or investigational device within 4 weeks prior to the first dose.
• Use of immunosuppressive agents within 14 days prior to the first dose of study treatment.
• Presence of other uncontrolled serious medical conditions.

Patient initially diagnosed with extensive small cell lung cancer at the First Hospital of Jilin University.