Tislelizumab Combined with SOX Regimen in the Treatment of Locally Advanced Gastric Cancer/gastroesophageal Junction Adenocarcinoma

Inclusion Criteria:

1. Willing to participate in this study, able to sign the informed consent form, andwith compliance;

2. No gender restriction, aged ≥18 and ≤70 years (at the time of signing the informedconsent form);

3. ECO score of 0-1;

4. Estimated survival ≥6 months;

5. HER-2 negative;

6. Central laboratory confirmed PD-L1 expression in the, with a combined positive score (CPS) ≥1;

7. Histological and radiological assessment confirmed as advanced gastric cancer (GC)or gastroesal junction (GEJ) adenocarcinoma, with a clinical stage of cT3-T4aN M0;

8. Pre-enrollment by the attending physician to determine eligibility for R0 resectionwith curative intent;

9. Good cardiac function. Patients with underlying ischemic, valvular disease, or othersevere heart disease should have a preoperative assessment by a cardiologist ifthere are clinical indications;

10. No prior cytotoxic or targeted, no prior partial or complete esophagogastric tumorresection;

11. Negative for hepatitis B surface antigen (HBsAg) and hepatitis core antibody (HBcAb). If HBsAg is positive or HBcAb is positive, then the hepatitis B virusdeoxyribonucleic acidHBV-DNA) must be <1000 copies/mL or <200 IU/mL or <the upperlimit of normal (ULN) at research center to be eligible;

12. Negative for hepatitis C virus (HCV) antibody;

13. Normal major organ function, as defined by the criteria (within 14 days before thefirst dose, without transfusions, albumin, recombinant human thrombopoietin, orcolony-stulating factor (CSF) treatment): Blood routine examination: Hemoglobin (Hb) ≥90g/L; absolute neutrophil count (ANC ≥1.5×109/L; platelets (PLT) ≥80×109/L;Biochemical examination: Alanine aminotransferase (ALT) and aspartateaminotransferase (AST) ≤2.5×ULN (≤5×ULN liver metastasis); total bilirubin (TBIL) ≤1.5×ULN (≤3×ULN for Gilbert's syndrome); seruminine (Cr) ≤1.5×ULN, or creatinineclearance rate ≥60mL/min; Coagulation function: Activated partialboplastin time (APTT), international normalized ratio (INR), and prothrombin time (PT) ≤1.5×ULN;Dpler ultrasound assessment: Left ventricular ejection fraction (LVEF) ≥50%; Normalthyroid function, defined as thyroid-stimulating hormone (T) within the normalrange. If baseline TSH is out of range, patients with total T3 (or FT3) and FT4within the normal range also be included; Clinical judgment by the doctor that organfunction is sufficient.

14. Fertile subjects must use appropriate contraception during the study and for 20 daysafter the study ends, have a negative serum pregnancy test within 7 days beforeenrollment, and must not be breastfeeding

Exclusion Criteria:

1. Have had or simultaneously have other active malignant tumors within 5 years. Curedlocalized tumors, as basal cell carcinoma of the skin, squamous cell carcinoma ofthe skin, superficial bladder cancer, prostate carcinoma in situ, cervical carcinomain situ, and breast in situ, are eligible;

2. Patients who are preparing for or have previously undergone organ or bone marrowtransplantation;

3. Have ≥2 grade myocardial ischem or myocardial infarction, arrhythmia (QTc ≥470ms),and ≥2 grade congestive heart failure (New York Heart AssociationNYHA]classification);

4. Human immunodeficiency virus (HIV) infection;

5. Have active pulmonary tuberculosis;

6. Have a history or current presence interstitial pneumonia, pneumoconiosis, radiationpneumonia, drug-related pneumonia, severe pulmonary dysfunction, etc., which mayinterfere with the detection and management of suspected drug-related pulmonarytoxicity;

7. Have known active or suspected autoimmune diseases, except those in a stable stateat the time of enrollment (not requiring systemic immunospressive therapy);

8. Have received live vaccine treatment within 28 days before the first dose; seasonalflu vaccines are not included;

9. Have received or need receive systemic corticosteroids (> 10 mg/day prednisoneequivalent dose) or other immunosuppressive drugs within 14 days before the dose orduring the study. However, the following cases are allowed: patients with no activeautoimmune diseases can use topical or inhaled corticosteroids, or hormonereplacement therapy with a dose ≤ 10 mg/day prednisone equivalent dose;

10. Have any active infection that requires systemic anti-infective within 14 daysbefore the first dose; prophylactic antibiotic treatment (e.g., for urinary tractinfections or chronic obstructive pulmonary disease) is not;

11. Have previously received other antibodies/drugs targeting immune checkpoints, suchas PD-1, PD-L1, CTLA4, etc.;

12. Are currently receiving other clinical study treatments, or the time between the endof the previous clinical study treatment and the planned start of this studytreatment is less than14 days;

13. Have a known severe allergic history to any monoclonal antibody or excipients of thestudy drug;

14. Have a history of psychiatric drug abuse or drug addiction; patients who havestopped drinking alcohol can be enrolled; According to the investigator's judgment,patients with serious concomitant that endanger the safety of the subjects or affectthe completion of the study, or patients who are deemed unsuitable for enrollmentfor other reasons