A Study to Evaluate Serplulimab in Combination With Docetaxel +S-1 VS. Docetaxel +S-1 as Adjuvant Treatment Therapy in Stage IIIc Gastric Cancer

Inclusion Criteria:

• The patients voluntarily joined the study and signed the informed consent; ≥ 18 yearsold, ≤ 75 years old, both male and female; Stage III gastric cancer confirmed bypathology, ECoG score: 0-1 Detection of biomarkers in postoperative gastric cancersamples suggests that: PD-L1 + CPS ≥ 5 / MSI-H + / EBV+/dMMR No preoperativeanti-tumor treatment for gastric cancer, including chemotherapy and local treatmentDuring the study treatment period and within 3 months after the end of the studytreatment period, a medically recognized contraceptive measure (such as IUD,contraceptive pill or condom) should be used for the female patients of non-surgicalsterilization or childbearing age; the serum or urine HCG test of the female patientsof non-surgical sterilization must be negative within 72 hours before the study group;and the hCG test must be non lactation; for the male patients Sex, should be surgicalsterilization, or agree to use appropriate methods of contraception during the trialand within 3 months after the last administration of the test drug. The baseline blood routine and biochemical indexes of the selected patients should meet thefollowing standards:

A. hemoglobin ≥ 90g / L

B. absolute neutrophil count ≥ 1.5 × 10 ^ 9 / L C. platelet count ≥ 100 × 10 ^ 9 / L D. ASTor ALT ≤ 2.5 ULN

E. Alkaline phosphatase (ALP)≤ 2.5×ULN TSH ≤ 1 ULN (if abnormal, T3 and T4 levels should be examined at the same time, if T3 andT4 levels are normal, they can be included in the group);

Exclusion Criteria:

• Pregnant or lactating women; Women of childbearing age were positive in the baselinepregnancy test; Distant metastasis was diagnosed by CT /MR/ EUS. Received previousanti-tumor treatment, including chemotherapy, radiotherapy or immunotherapy; Haveother malignant tumors in the past 5 years (except basal cell or squamous cellcarcinoma, superficial bladder cancer, cervical cancer in situ or breast cancer);Uncontrollable pleural effusion, pericardial effusion or ascites; Severecardiovascular diseases such as symptomatic coronary heart disease, congestive heartfailure ≥ level II, uncontrolled arrhythmia and myocardial infarction within 12 monthsbefore admission; With gastroduodenal obstruction/bleeding, digestive dysfunction ormalabsorption syndrome Complicated with severe uncontrolled concurrent infection orother serious uncontrolled concomitant diseases, moderate or severe renal injury;Allergic reaction to the drugs used in this study; Steroid or other systemicimmunosuppressive therapy was used 14 days before admission; Patients who receivedstudy drug treatment within 4 weeks before enrollment (participate in other clinicaltrials). Active autoimmune diseases (including but not limited to: uveitis, enteritis, hepatitis,hypophysitis, nephritis, vasculitis, hyperthyroidism, hypothyroidism and asthma requiringbronchodilator treatment). Subjects with hypothyroidism requiring only hormone replacementtherapy and skin diseases without systemic treatment (such as vitiligo, psoriasis oralopecia) can be selected. History of primary immunodeficiency. Immunosuppressive drugs were used within 4 weeks priorto the first dose of study treatment, excluding local or physiological doses of systemicglucocorticoids (i.e. no more than 10mg / day of prednisone or other glucocorticoids ofequivalent dose) by nasal spray, inhalation or other routes, or hormones used to preventallergy of contrast agents. Receive live attenuated vaccine within 4 weeks before the first dose of study treatment orduring the study period. Active tuberculosis is known. We have known the history of allogeneic organ transplantationand allogeneic hematopoietic stem cell transplantation. HIV antibody positive, active hepatitis B or C (hepatitis B: HBsAg positive and HBV DNA ≥ 10 ⁴ copies / ml; hepatitis C: HCV antibody and HCV-RNA positive, requiring antiviraltreatment at the same time);. Other factors that may affect the safety or test compliance of the subjects according tothe judgment of the researchers. For example, serious diseases (including mental diseases)requiring combined treatment, serious laboratory abnormalities, or other family or socialfactors, etc.