PD-1 Monoclonal Antibody Combined With FLOT Regimen for Neoadjuvant Therapy of Gastric Adenocarcinoma

Inclusion Criteria: * Informed consent has been signed; * Only patients aged 18-75 were enrolled; * Pathologically confirmed gastric adenocarcinoma (cT4 or/and N+M0, MDT considers perioperative treatment necessary) :Bone scan should be performed if bone metastasis is suspected.If peritoneal metastasis is suspected, laparoscopy should be performed; * No previous cytotoxic chemotherapy or targeted therapy; * No previous local resection of the tumor; * ECOG 1 or less; * Tumor specimens capable of detecting PDL-1 and MSI status are available.The detection of PDL-1 and MSI will be conducted after random grouping.This test requires the patient to provide a paraffin-embedded biopsy specimen; * Leukocyte ≥ 4×109/L, platelet ≥ 100×109/L without transfusion, absolute value of neutrophils (ANC) without granulocyte stimulation factor ≥ 1.5×109/L, and hemoglobin≥ 90 g/L; * Bilirubin ≤ 1.5 times of the upper limit of normal value, and rice grass and rice propyl transaminase ≤ 2.5 times of the upper limit of normal value; * Serum creatinine ≤ 1.5 times the upper limit of normal value, or GFR\>45ml/min; * Serum albumin ≥ 25g /L (2.5g /dL); * INR or aPTT ≤1.5 times ULN; Exclusion Criteria: * Allergy to any experimental drug and its excipients, or a history of severe allergy, or a contraindication to the experimental drug; * Ahistory of autoimmune diseases or active stage; * Previous allogeneic bone marrow transplantation or organ transplantation; * Congenital pulmonary fibrosis, drug-induced pneumonia, organized pneumonia, or ct-confirmed active pneumonia; * HIV test positive; * Active hepatitis b or c; * Active tuberculosis; * Uncontrolled cancer pain; * Live attenuated vaccine was injected within 4 weeks before the study began, or live attenuated vaccine was expected to be injected during the trial or within 5 months after the trial; * Previous immunotherapy, including CTLA4, anti-pd-1, or anti-pdl1 monoclonal antibody; * CT suggested active pulmonary inflammation; * Systemic application of glucocorticoids or immunosuppressants within 2 weeks before the start of the trial.Inhaled glucocorticoids and glucocorticoids are allowed; * There are taboos on hormone use; * Severe cardiovascular disease, myocardial infection or cerebrovascular accident, arrhythmia, unstable angina within 3 months before the start of the trial; * Uncontrolled increase in blood pressure or blood sugar; * Other malignancies prior to 5 years, with the exception of cervical carcinoma in situ, non-melanoma skin cancer, or stage I uterine cancer; * Known central nervous system metastases; * Peripheral neuropathy ≥ NCI CTCAE grade 2; * Serum albumin below 2.5 g/dL; * Uncontrolled or symptomatic hypercalcemia; * Infections requiring antibiotics within 14 days prior to the start of the trial; * Chronic enteritis; * Clinically significant active gastrointestinal bleeding; * Non-diagnostic surgery within 4 weeks before the start of the trial; * Any other disease where there is evidence of a need to restrict the use of the experimental drug; * Participate in other tests within 30 days before the start of the test, or plan to participate in other tests during the test; * Receive other experimental drugs within 28 days prior to the start of the trial; * Pregnantor lactating women, or women who plan to become pregnant within 5months after the end of treatment.Women of childbearing age should undergo a blood pregnancy test within 7 days of the start of the trial.