Inclusion Criteria:
1.Age:18-75 years old, male or female; 2.Pathologically confirmed Siewert Type II adenocarcinoma of the gastroesophageal junction; 3.Clinical stage cT3-4aN1-3M0; 4.Low to moderate HER2 expression or no expression (IHC 2+ and FISH- / IHC 1+ / IHC -)； 5.Eastern Cooperative Oncology Group (ECOG) performance status of 0-1; 6.At least one measurable lesion (according to RECIST 1.1 criteria)； 7.Expected survival ≥ 3 months; 8.Normal functioning of major organs, i.e. meeting the following criteria:
1. routine blood tests:
1. HB≥90g/L；
2. ANC≥1.5×109/L；
3. PLT≥100×109/L；
2. biochemical examination:
1. ALT and AST\<2.5ULN（liver metastasis: ALT and AST\<5ULN）；
2. TBIL≤1.5ULN；
3. Creatinine ≤1.5ULN； 9.Left ventricular ejection fraction is \>50%； 10.Women of childbearing potential must have a negative pregnancy test (serum or urine) within 14 days prior to enrollment and must agree to use appropriate contraception during the observation period and for 8 weeks following the last administration of the study drug; for men, they must be surgically sterilized or agree to use appropriate contraception during the observation period and for 8 weeks following the last administration of the study drug; 11. Participants were willing to join in this study, written informed consent, good adherence and co-operation with follow up.
Exclusion Criteria:
1. Known signs of active bleeding from the lesion (except for a positive fecal occult blood test);
2. Diagnosis of HER2-positive adenocarcinoma of the stomach or gastroesophageal junction;
3. Cardia or pyloric obstruction;
4. Currently participating in an interventional clinical trial, or having received treatment with another investigational drug or device within 4 weeks prior to the first dose;
5. Known hypersensitivity to any monoclonal antibody or component of a chemotherapy agent (such as tegafur or albumin-bound paclitaxel) (history of Grade 3 or higher hypersensitivity reaction);
6. Previous exposure to any anti-PD-1 or anti-PD-L1, PD-L2, CD137, or CTLA-4 antibody therapy, or any other antibody or drug specifically targeting T-cell co-stimulation or checkpoint pathways;
7. Receipt of an attenuated live vaccine within 4 weeks prior to the first dose of study treatment, or planned administration during the study period;
8. Use of immunosuppressants or systemic corticosteroids for immunosuppressive purposes within 14 days prior to the start of study treatment (dose \> 10 mg/day of prednisone or other corticosteroids of equivalent potency);
9. History of active autoimmune disease requiring systemic treatment within 2 years prior to the first dose;
10. Congenital or acquired immunodeficiency (e.g., HIV infection);
11. The investigator determines that the subject has other factors that may affect the study results or lead to the premature termination of the study, such as alcohol abuse, substance abuse, other serious illnesses (including mental disorders) requiring concomitant treatment, severe laboratory abnormalities, or family or social factors that may compromise the subject's safety;
12. Pregnant or breastfeeding women;
13. Evidence of medical history or disease that may interfere with trial results or prevent the subject from participating in the study throughout its duration, abnormal treatment or laboratory test results, or other circumstances deemed by the investigator to make the subject unsuitable for enrollment; or other potential risks identified by the investigator that render the subject unsuitable for participation in this study.
