This study is a multi-center, Single-arm Phase II study to evaluate the clinical efficacy and safety of Consolidation HLX10 (Serplulimab) Following Hypofractionated Radiotherapy With Concurrent Chemotherapy for Patients With Limited Stage Small Cell Lung Cancer

All eligible patients after screening will receive up to four cycles chemotherapy. Recommended regimens are etoposide 100 mg/m2 intravenously on day 1-3 in combination with cisplatin 75 mg/m2 intravenously on day 1 or carboplatin AUC=5 every 3 weeks.

A total of 45Gy in 15 fractions over 3 weeks will be delivered. PCI is routinely scheduled for patients without progression after chemoradiotherapy, and hippocampal avoidance is highly recommended. 25Gy in 10 fractions over 2 weeks to the brain will be prescribed. Intensity modulated radiation therapy (IMRT) or volumetric modulated arc therapy (VMAT) technique are required. Patients without disease progression will receive an intravenous infusion of serplulimab 300mg every 3 weeks. Treatment of serplulimab should be continued until disease progression, intolerable toxicity, withdrawal of consent, or to a maximum of 1 year. Continuation of immunotherapy after disease progression is acceptable per investigators' discretion.

The investigator and IRRC respectively assess the tumor images according to RECIST 1.1.

Inclusion Criteria:

1. Age 18-75 years; ECOG score 0-1.
2. Histologically or cytologically confirmed small cell lung cancer.
3. Limited stage, defined as the tumor confined to one side of the thoracic cavity including ipsilateral hilar, bilateral mediastinal, and bilateral supraclavicular lymph nodes, (metastatic lymph nodes are defined as short diameter ≥ 1 cm or increased metabolism on PET-CT considering metastatic lymph nodes); unless cytologically confirmed malignant pleural effusion, the thickness of pleural effusion on chest CT is less than 1 cm; (stage I-IIIB without intrapulmonary metastasis in the 7th edition of AJCC staging in 2009) .
4. No other previous anti-tumor history, at least 3 months of expected survival.
5. No serious medical diseases and dysfunction of major organs, such as blood routine, liver, kidney, heart and lung function.

Exclusion Criteria:

1. Histologically or cytologically confirmed mixed SCLC.
2. Subjects suitable for surgery. Subjects who are suitable for surgery but refuse surgical treatment can be included.
3. Patients who have previously received systematic anti-tumor treatments for small cell lung cancer, including but not limited to radiotherapy, chemotherapy, and immunotherapy.
4. Patients with other active malignancies within 5 years or at the same time.
5. Subjects with known history of severe allergy to any monoclonal antibody.
6. Subjects with known anaphylaxis to carboplatin/cisplatin or etoposide.
7. In the judgment of the investigator, subjects who have any other factors that may lead to a premature discontinuation.