Exploratory Clinical Study of Penpulimab Combined With SOX in the Perioperative Treatment of Gastric Cancer

Inclusion Criteria: * signed and dated informed consent; * At least 18 years of age; * ECOG PS: 0-1; * Patients with gastric cancer diagnosed as T3-4NXMX by imaging; * Patients with gastric adenocarcinoma diagnosed by cytology; * Patients with gastric cancer assessed by the surgeon as suitable for neoadjuvant therapy or conversion therapy followed by radical resection; * Laboratory tests should meet the following requirements (28 days before enrollment in baseline period) : * Women should agree that they must use contraception during and for 6 months after the study; Had a negative serum pregnancy test within 7 days prior to study enrollment and had to be non-lactating; Men should agree that they must use contraception during the study and for 6 months after the end of the study period. Exclusion Criteria: * Co-existing with other malignant tumors (except cured basal cell carcinoma of the skin); * Gastric cancer patients with T1-2N0M0; * Previous treatment including anti-PD-1 /PD-L1/CTLA-4 antibody therapy or other immunotherapy directed against PD-1/PD-L1/CTLA-4; * Weight loss greater than or equal to 20% within 4 weeks before the first dose; * Severe hypersensitivity after administration of other monoclonal antibodies; * The presence or history of any active autoimmune disease * Immunosuppressive therapy, systemic or absorbable local hormone therapy (dose \> 10mg/ day prednisone or other effective hormone) is required to achieve immunosuppression and continues to be used within 2 weeks of the first administration; * Patients with multiple factors affecting oral medication * Uncontrolled pleural effusion, pericardial effusion, or ascites that require repeated drainage; * Had received a prophylactic or attenuated vaccine within 4 weeks before the first dose;