Fruquintinib Combined With Toripalimab and SOX Regimen in the First-line Treatment of Advanced Metastatic Gastric or Gastroesophageal Junction Adenocarcinoma

Inclusion Criteria: * Pathologically determined unresectable advanced gastric or gastroesophageal junction adenocarcinoma; * 18-75 years old (including 18 and 75 years old); * No previous anti-tumor treatment for metastatic diseases; * HER2 negative; * Eastern Cooperation Oncology Group (ECOG) performance status of 0-1; * Life expectancy ≥ 3 months; * At least one measurable lesion according to RECIST version 1.1; * Adequate organ and bone marrow functions: Absolute neutrophil count≥1.5x10\^9/L; Platelet count≥100x10\^9/L; Hemoglobin≥9g/dL; Serum bilirubin≤1.5x the upper limit of normal(ULN); Alanine aminotransferase(ALT) and aspartate aminotransferase(AST)≤1.5x ULN; Serum creatinine≤1.5x ULN; Endogenous creatinine clearance rate ≥ 50ml / min; * Women of childbearing age need to take effective contraceptive measures. Exclusion Criteria: * Previous treatment with vascular endothelial growth factor receptor (VEGFR) inhibitors or previous use of immune checkpoint inhibitors; * Other malignant tumors in the past 5 years, except for skin basal cell or squamous cell carcinoma after radical surgery, or cervical carcinoma in situ; * There was central nervous system (CNS) metastasis or previous brain metastasis before enrollment; * Patients with autoimmune diseases or history of autoimmune diseases within 4 weeks before enrollment; * Previously received allogeneic bone marrow transplantation or organ transplantation; * Uncontrolled malignant ascites; * Participated in other unapproved or unlisted drug clinical trials in China within 4 weeks before enrollment, and received corresponding experimental drug treatment; * Cardiovascular disease, including unstable angina or myocardial infarction, occurred within 6 months before the start of study treatment; * Subjects allergic to the study drug or any of its adjuvants; * International normalized ratio (INR) \> 1.5 or partially activated prothrombin time (APTT) \> 1.5 × ULN； * The researchers judged clinically significant electrolyte abnormalities; * At present, the patient has hypertension that cannot be controlled by drugs, which is specified as: systolic blood pressure ≥ 140 mmHg and / or diastolic blood pressure ≥ 90 mmHg; * Patients currently have poorly controlled diabetes (fasting glucose level is greater than CTCAE grade 2 after regular treatment); * Patients with dysphagia, active peptic ulcer, intestinal obstruction, active gastrointestinal bleeding, peptic perforation, malabsorption syndrome or uncontrolled intestinal inflammatory diseases; * Any disease or state affecting drug absorption before enrollment, or the patient cannot take oral medication; * Patients with obvious evidence of bleeding tendency or medical history within 3 months before enrollment, hemoptysis or thromboembolism within 12 months; * Cardiovascular diseases with significant clinical significance, including but not limited to acute myocardial infarction, severe / unstable angina pectoris or coronary artery bypass grafting within 6 months before enrollment; * Ventricular arrhythmia requiring drug treatment; * Congestive heart failure ≤New York Heart Association (NYHA) class 2; * LVEF \< 50%; * Active or uncontrolled severe infection ≥ grade 2 according to National Cancer Institute Common Toxicity (NCI-CTC) criteria; * With positive urine protein and 24-hour urinary protein content\>1g; * Known human immunodeficiency virus (HIV) infection; known history of clinically significant liver disease, including viral hepatitis; * Pregnant (positive pregnancy test before medication) or lactating women; * Complications require long-term immunosuppressive treatment, or systemic or local use of immunosuppressive corticosteroids (\> 10mg / day prednisone or other therapeutic hormones); * By judgment of the investigator, there are concomitant diseases that seriously endanger the safety of the patient or affect the completion of the study.