PD-1 Antibody Adjuvant Therapy for GC Patients With MSI-H After D2 Radical Surgery

"Drug: Tegafur-Gimeracil-Oteracil Potassium The dose of S-1 is according to body-surface area (BSA): patients with a BSA of less than 1.25 m2 received 80 mg daily; those with a BSA of 1.25 m2 or more but less than 1.5 m2 received 100 mg daily; and those with a BSA of 1.5 m2 or more received 120 mg daily. oxaliplatin 130mg/m2, intravenously, on day 1.~Drug: Oxaliplatin The dose of oxaliplatin is according to body-surface area (BSA): 130mg/m2, intravenously, on day 1."

Drug: Capecitabine 1000mg/m2, orally, twice per day, from day 1 to day 14, Q3W. Drug: Oxaliplatin The dose of oxaliplatin is according to body-surface area (BSA): 130mg/m2, intravenously, on day 1.

follow up and Observation alone. Abdomen/chest CT scan will be performed every 6 months after surgery.

Sintilimab at a dose of 200 mg every 3 weeks for 16 cycles or Nivolumab at a dose of 360 mg every 3 weeks for 16 cycles