This is an open-label, single arm Phase II study designed to evaluate the efficacy and safety of thoracic radiotherapy for extensive-stage small-cell lung cancer treated with PD-1/PD-L1 plus etoposide platinum followed by PD-1/PD-L1 maintenance therapy

This study a single arm prospective phase II study. All the enrolled patients will be patients with ES-SCLC who did not have PD (determined as per the RECIST v1.1) after 6 cycle of platinum-based chemotherapy in combination with an anti-PD-1/L1. Then, those enrolled patients would be treated with thoracic radiotherapy concurrently with PD-1/PD-L1 maintenance therapy, and the total maintenance therapy time should at least more than 6 months.

Inclusion Criteria:

1. Age between18 years and 80 years at time of study entry
2. ECOG performance status of 0 or 1
3. Body weight >30 kg
4. Adequate bone marrow, liver and kidney function
5. Life expectancy of at least 3 months
6. At least one measurable (RECIST 1.1), thoracic lesion that can be irradiated with 45 Gy/15 fractions
7. Histologic or cytologic confirmation of small cell lung cancer
8. Stage III-IV disease (TNM v8)
9. Adequate pulmonary function with FEV1 >1 L or >30 % of predicted value and DLCO >30 % of predicted value
10. Patients with brain metastases are eligible provided they are asymptomatic or treated and stable on steroids and/or anticonvulsants prior to the start of treatment -

Exclusion Criteria:

1. Previous chemo-, immuno- or radiotherapy for SCLC
2. Major surgical procedure last 28 days
3. History of allogenic organ transplantation, autoimmune disease, immunodeficiency, hepatitis or HIV
4. Uncontrolled intercurrent illness
5. Other active malignancy
6. Leptomeningeal carcinomatosis
7. Immunosuppressive medication
8. Pregnant or breastfeeding women