PD-1 Inhibitors Consolidation in Extensive-stage Small Cell Lung Cancer

Inclusion Criteria:

* Sign written informed consent;
* With extensive small cell lung cancer;
* Previously received first-line standard chemotherapy, with treatment response of CR or PR;
* Can provide at least 5-8 pathological tissue specimens (for detecting PD-L1 expression and infiltrating lymphocytes)
* Can tolerate the radiotherapy process;
* Weight ≥ 40kg;
* Life expectancy ≥ 12 weeks;
* With the Eastern Cancer Cooperative Group (ECOG) score 0-1;
* The interval from the previous chemotherapy is more than 4 weeks, the grade of all adverse events caused by previous treatment have been reduced to grade 1 or less evaluated by CTCAE 4.03;
* Before the administration of the study drug, systemic drugs (such as corticosteroids) applied at an immunosuppressive dose level (prednisone \> 10 mg/d or equivalent) must have been discontinued for at least 2 weeks;
* Major surgery requiring general anesthesia must have been completed for at least 4 weeks before administration of the study drug. Surgery requiring local anesthesia/epidural anesthesia must have been completed for at least 72 hours before administration of the study drug, and the subject must have recovered. Skin biopsy with only local anesthesia has been completed for at least 1 hour before administration of the study drug.
* Other criteria including the laboratory values meets the requirements specified in the protocol.

Exclusion Criteria:

* Subjects with central nervous system (CNS) metastases;
* The subject has cancerous meningitis;
* Subjects with active, known or suspected autoimmune diseases ;
* Previously treated with anti-PD-1 antibody, anti-PD-L1 antibody, anti-PD-L2 antibody or anti-CTLA-4 antibody (or any other antibody acting on the T cell stimulation or checkpoint pathway);
* According to chest X-ray examination, sputum examination and clinical examination, it is determined that there is active tuberculosis (TB) infection now or before, even one year before;
* A positive immunodeficiency virus (HIV) test or have acquired immunodeficiency syndrome (AIDS);
* With comorbidity needs to be treated with an immunosuppressive drug;
* Other research drugs were administrated 28 days prior to the start of study drug or although they were more than 28 days apart, still within the 5 half-life of previous study drugs;
* Inoculated with any anti-infective vaccine (such as influenza vaccine, varicella vaccine, etc.) within 4 weeks before starting the study drug;
* In the condition of pregnant or breastfeeding;
* Inability to tolerate venous puncture and/or venous access;
* Any other medical, psychotic, and/or social problems determined by the investigator;
* Subject has interstitial lung disease;
* Use any Chinese medicine with anti-tumor activity within 2 weeks before starting of the study drug;
* Monoclonal antibodies have been used in the past 3 months, except for topical use;
* Subjects who have previously had other malignancies (excluding non-melanoma skin cancer and the following carcinomas in situ: bladder, stomach, colon, endometrium, cervix/dysplasia, melanoma or breast cancer) are not allowed to participate in the study. Unless he/she has been cured at least 2 years prior to enrollment, and does not require additional treatment or other treatments during the study;
* Subjects with chronic hepatitis B (hepatitis B surface antigen positive) or chronic hepatitis C (HCV antibody positive) blood screening positive;
* Previously allergic to macromolecular protein preparations, or to any of the JS001 ingredients.