A Study of Sintilimab or Placebo in Combination With Chemotherapy as Second-line Treatment for Patients With Stage IV Nonsquamous Non-small Cell Lung Cancer With Wild-type EGFR After Failure With Platinum-Containing Chemotherapy.

Inclusion Criteria:

1. Volunteer to participate in clinical research; fully understand and know the research and sign informed consent;
2. Age ≥ 18 years old and ≤ 75 years old, either sex;
3. Eastern Collaborative Oncology Group Performance status (ECOG PS) 0, 1 or 2;
4. Has a histologically or cytologically confirmed diagnosis of stage IV (according to the 8th edition of the International Association for the Study of Lung Cancer) nonsquamous NSCLC;
5. Have at least one measurable lesion as defined by RECIST 1.1;
6. Has progression of disease after treatment with at least two cycles of a platinum-containing doublet chemotherapy according to RECIST V.1.1;
7. Patients without activating EGFR mutation;
8. Normal hepatic function: total bilirubin≤1.5×normal upper limit (ULN); Alanine aminotransferase and Aspartate aminotransferase levels ≤2.5×ULN or ≤5×ULN if liver metastasis is present;
9. Normal renal function: Creatinine ≤1.5×ULN or calculated creatinine clearance ≥45 mL/min (using Cockcroft/Gault formula to calculate );
10. Normal hematological function: absolute neutrophil count ≥1.5×109/L, platelet count ≥70×109/L, hemoglobin≥80g/L \[no blood transfusion or erythropoietin (EPO) within 7 days\] Dependency\];
11. Has a life expectancy of at ≥3 months.

Exclusion Criteria:

1. ECOG PS \>2;
2. Small cell lung cancer and squamous NSCLC;
3. EGFR mutation or mutation status unknown;
4. Known hypersensitivity or allergy to monoclonal antibody;
5. Prior therapy with an anti-programmed cell death (PD)-1, anti-PD-L1, anti-PD-L2, anti-tumor necrosis factor CD137, or anti-cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) antibody (including any other antibody or drug specifically targeting T-cell co-stimulation or checkpoint pathways);
6. Active autoimmune disease, or a documented history of autoimmune disease;
7. Treatment with systemic corticosteroids (prednisone≥10mg per day or equivalent dose) or other systemic immunosuppressive medications within 2 weeks prior to the first dose;
8. Known history or active human immunodeficiency virus (HIV);
9. Known acute or chronic active hepatitis B (HBV DNA positive) infection or acute or chronic active hepatitis C (HCV antibody positive and HCV RNA positive) infection;
10. Interstitial lung disease, or history of pneumonitis requiring systemic steroids for treatment;
11. Active or poorly controlled severe infection;
12. Have serious cardiovascular disease: Symptomatic congestive heart failure (New York Heart Association grade III-IV), unstable angina pectoris, unstable arrhythmia, myocardial infarction or cerebrovascular accident within 3 months before randomization;
13. Received thoracic radiation therapy of \>30 Gy within 6 months prior to first dose of study drug;
14. Completed palliative radiotherapy within 7 days prior to first dose of study drug;
15. Pregnant or lactating women.