Conversion Therapy of Sintilimab in Combination With Apatinib and Chemotherapy in Stage IV Gastric Cancer

Inclusion Criteria: * gastric adenocarcinoma confirmed by gastroscopy and pathology (histologically/cytologically ) ; * life expectancy of ≥3-month； * unresectable patients who were initially diagnosed as stage IV (clinical stage, American Joint Committee on Cancer 8th edition); * Eastern Cooperative Oncology Group performance status: 0-1; * must have at least 1 of the following unresectable factors indicated by CT, MRI or positron emission tomography(PET)-CT: 1. N3 lymphatic metastasis; 2. Extensive or bulky lymph nodes; 3. T4b; 4. Hepatic metastasis: ≤5 lesions, total diameter of ≤8cm; 5. Peritoneal metastasis (CY1, P1); 6. Kukernburg tumor; * adequate organ function; * pregnant test negative of females of childbearing potential , and willing to use adequate contraception; * written Informed Consensus Form; Exclusion Criteria: * prior use of any checkpoint inhibitor treatment, including PD-1, programmed cell death ligand-1(PDL-1), CTLA4 etc; * Her-2 positive with willing to use herceptin treatment; * prior active autoimmune disease or history of autoimmune disease; * clinically significant cardiovascular and cerebrovascular diseases, including but not limited to severe acute myocardial infarction within 6 months before enrollment, unstable or severe angina, or coronary artery bypass surgery, Congestive heart failure (New York heart association (NYHA) class \> 2), ventricular arrhythmia which need medical intervention, left ventricular ejection fraction(LVEF) \< 50%; * not controlled hypertension; * prior systemic treatment to metastatic disease； * previous digestive tract bleeding history within 3 months or evident gastrointestinal bleeding tendency; * history of immunodeficiency including seropositivity for human immunodeficiency virus (HIV), or other acquired or congenital immune-deficient disease, or active hepatitis ; * patients who may receive vaccination during study period; * mental disorders history, or psychotropic drug abuse history; * unable to orally administration;