Tislelizumab Combined With Apatinib and Oxaliplatin Plus S1 Vs Oxaliplatin Plus S1 as Neoadjuvant Therapy for Borrmann IV、Large Borrmann III Type and Bulky N Positive Advanced Gastric Cancer

Inclusion Criteria: * Age: 18-70 years of age. * Histologically confirmed gastric adenocarcinoma was diagnosed in patients with locally advanced gastric cancer with tumor volume \>5cm Borrmann III, Borrmann IV and BulkyN according to AJCC Version 8. * Measurable lesions at least should be detected by CT/MRI examination in accordance with the RECIST1.1. * ECOG（Eastern Cooperative Oncology Group）PS（Performance Status）:0-1 scores. * No previous surgical treatment, anti-tumor chemoradiotherapy/immunotherapy was performed. * Preoperative endoscopic examination confirmed no positive peritoneal implantation metastasis and exfoliated cells. * The expected survival time is more than 6 months. * For women of reproductive age, a urine or serum pregnancy test with negative results should be performed within 3 days prior to receiving the first study drug administration (day 1 of cycle 1).If a urine pregnancy test result cannot be confirmed as negative, a blood pregnancy test is requested.Women of childbearing age were defined as at least 1 year after menopause or having undergone surgical sterilization or hysterectomy. Exclusion Criteria: * Diagnosis of malignant diseases other than gastric cancer within 5 years prior to first administration (excluding radical basal cell carcinoma of the skin, squamous carcinoma of the skin, and/or radical resectable carcinoma in situ). * Significant clinical bleeding symptoms or clear bleeding tendency, such as gastrointestinal bleeding, hemorrhagic gastric ulcer or vasculitis, etc. occurred within 3 months before enrollment. If fecal occult blood was positive at baseline, reexamination could be performed，if it was still positive after reexamination, gastroscopy was required. * Prior treatment: anti-PD-1, anti-PD-L1, or anti-PD-L2 drugs or drugs that target another stimulating or co-inhibiting T-cell receptor (e.g., CTLA-4, OX-40, CD137). * A history of immunodeficiency, including HIV testing positive. * Is currently participating in an interventional clinical study or has been treated with another study drug or study device in the 4 weeks prior to initial dosing. * Patients who had a history of cardiovascular and cerebrovascular diseases and were still taking thrombolytic drugs or anticoagulants orally. * HER2 positive is known. * Patients with previous gastrointestinal perforation, abdominal abscess or recent intestinal obstruction (within 3 months) or imaging or clinical symptoms suggesting intestinal obstruction.