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.