A Phase II Clinical Study of Fruquintinib Combined With RC48 in the Treatment of Previously Treated HER2-positive Locally Advanced or Metastatic Gastric or Gastroesophageal Junction (G/GEJ) Cancer

Inclusion Criteria: 1. Aged 18-75years (inclusive); 2. Body weight ≥40 kg; 3. Physical status score (ECOG score) 0-1; 4. Expected survival \>12 weeks.; 5. At least one measurable lesion (according to RECIST1.1); 6. Histologically or cytologically confirmed diagnosis of locally advanced unresectable or metastatic HER2 positive G/GEJ cancer; 7. HER2-positive defined as either immunohistochemistry (IHC) 3+ or IHC 2+ in combination with in-situ hybridization positive (ISH+) or fluorescent in-situ hybridization (FISH), as assessed by central review on primary or metastatic tumor; 8. Fail in previous first-line standard chemotherapy; 9. prior therapy does not need to have included a HER2-directed therapy; 10. Adjuvant or neoadjuvant therapy for AGC is allowed. 11. Absence of major post-operative complications or other clinical conditions that, in the opinion of the investigator, would contraindicate adjuvant chemotherapy 8. Adequate hematological function defined by absolute neutrophil count (ANC) ≥1.5 × 109/L, platelet count ≥100 × 109/L, and hemoglobin ≥9 g/dL (blood transfusion before recruitment is allowed) 12. Adequate hepatic function defined by a total bilirubin level ≤1.5 × the upper limit of normal (ULN) range and AST and ALT levels ≤2.5 × ULN 10. Adequate renal function defined by an estimated creatinine clearance ≥30 mL/min according to the Cockcroft-Gault formula (or local institutional standard method) 11. Negative serum or urine pregnancy test at screening for women of childbearing potential 12. Fertile men and women must agree to take highly effective contraceptive precautions during, and for 6 months after the last dose of chemotherapy or for 1 month after the last dose of Tislelizumab Exclusion Criteria: 1. An interval shorter than 21 days from the last dose of chemotherapy or HER2-directed therapy until the time of randomization 2. Prior treatment with RC48, Fruquintinib, or apatinib either as single agents or as part of a treatment regimen. 3. Treatment with any investigational anticancer drug within 21 days of the first study treatment administration 4. More than one prior line of therapy for advanced G/GEJ cancer; 5. History of other malignancy within the previous 5 years except for appropriately treated carcinoma in situ of the cervix, non-melanoma skin carcinoma, Stage I uterine cancer, or other malignancies with an expected curative outcome 6. Brain metastases that are untreated or symptomatic or require any radiation, surgery, or steroid therapy to control symptoms from brain metastases within 1 month of randomization 7. Peripheral neuropathy Grade \>/=2 8. Uncontrolled cardiopulmonary dysfunction (e.g., high blood pressure, serious cardiac arrhythmia) 9. Other current, severe, uncontrolled systemic disease (e.g., clinically significant metabolic disease, wound healing disorders, ulcers) 10. Clinically significant bleeding within 30 days before enrollment 11. For female participants, current pregnancy or lactation 12. Major surgical procedure or significant traumatic injury within 28 days prior to randomization or anticipation of the need for major surgery during the course of study treatment 13. Infection with Human immunodeficiency virus (HIV) or hepatitis B virus, hepatitis C virus