Fruquintinib Combined with Sintilimab As Second-line Therapy for Gastric or Gastro-esophageal Junction Adenocarcinoma

Inclusion Criteria: * Signed the Informed Consent Form * Ages: 18-75 Years (concluding 18 and 75 Years) * Pathologically confirmed unresectable advanced gastric/gastroesophageal junction adenocarcinoma * Failure to 1st line therapy, completed at least 28 days before enrollment * HER2-negative * Eastern Cooperative Oncology Group (ECOG) performance status 0-2 * Life expectancy greater than 3 months * At least one measurable lesion (larger than 10 mm in diameter by spiral CT scan, larger than 20 mm in diameter by conventional CT scan) according to RECIST1.1 * Sufficient organ functions as follows (any blood transfusion or cell growth factor use within 14 days before enrollment is not allowed): Absolute Neutrophil Count (ANC) ≥1.5×109/L Platelet Count of ≥175×109/L; Hemoglobin≥90g/L; Total Bilirubin (TBIL) ≤1.5 x ULN; ALT and /or AST\<1.5 x ULN; If there is liver metastasis, then ALT and/or AST\<3.0 x ULN; Serum Creatinine (SCr) ≤1.5×ULN; Endogenous creatinine clearance rate ≥50ml / min； * Man and woman who childbearing potential agrees to use adequate contraception * Willingness to provide enough tumor tissues for PD-L1 expression test Exclusion Criteria: * Patients could not obey the study protocol. * Previous therapy with VEGFR Inhibitor. * Other malignancy within 5 years prior to study enrolment, except for cervical carcinoma in situ, basal or squamous cell skin cancer. * Known brain or CNS metastases. * Patients with any active autoimmune disease or a documented history of autoimmune disease within 4 weeks prior to enrollment. * Prior allogeneic bone marrow transplantation or prior solid organ transplantation. * Uncontrolled malignant ascites. * Clinically significant cardiovascular diseases, including but not limited to acute myocardial infarction, severe / unstable angina pectoris or coronary artery bypass grafting within 6 months before enrollment; Congestive heart failure, New York Heart Association (NYHA) grade \> 2; ventricular arrhythmia requiring drug treatment; LVEF (left ventricular ejection fraction) \< 50%. * Known allergy or hypersensitivity to any of the study drugs or any of the study drug excipients. * Participation in another clinical trial with any experimental drug within 4 weeks prior to enrollment. * Clinically significant electrolyte abnormalities judged by researchers. * Systolic blood pressure \> 140mmHg or diastolic blood pressure \> 90mmHg regardless of any antihypertensive drugs. * Poorly controlled diabetes before enrollment. * Any factors that influence the usage of oral administration and patients cannot take fruquintinib orally. * Active gastric and duodenal ulcer, ulcerative colitis or uncontrolled hemorrhage in GI, or other conditions that may cause GI bleeding and perforation as determined by the investigator. * Patients with obvious evidence of bleeding tendency or medical history within 3 months before enrollment, hemoptysis or thromboembolism within 12 months. * Active infection or serious infection that is uncontrolled by drug (NCI CTCAE v. 5.0 Grade ≥ 2). * History of clinically significant hepatic disease, including hepatitis B virus (HBV) infection with HBV DNA positive (copies ≥1×104/ml or \>2000IU/ml); known hepatitis C virus infection with HCV RNA positive (copies ≥1×103/ml). * Persisting toxicity related to prior therapy (NCI CTCAE v. 5.0 Grade \> 1). * Pregnant or breastfeeding female patient. * Receive blood transfusion, blood products and hematopoietic factors such as albumin and granulocyte colony stimulating factor (G-CSF) within 14 days prior to enrollment. * Other severe acute or chronic medical conditions including metabolic disorder, physical examination or laboratory abnormalities that may increase the risk associated with study participation or study treatment administration or may interfere with the interpretation of study results and, in the judgment of the investigator, would make the patient inappropriate for entry into this study. * Urinary protein ≥ ++, and the 24-hour urine protein quantification is greater than 1.0 g. * Use of immunosuppressive medication, or systemic/local immunosuppressive corticosteroids for complication. * Patients considered unsuitable for inclusion in this study by the investigator.