Adaptive Adjuvant Therapy After Neoadjuvant Therapy and Gastrectomy for Gastric or Gastroesophageal Junction Adenocarcinoma

Prior treatment

• Inability to take oral medications.
• Underwent any surgery requiring general anesthesia that was not related to gastric cancer within 28 days before randomization.
• Active or prior autoimmune disease that may relapse or require immunosuppressive treatment within 2 weeks or during the study period; or a history of immunodeficiency, including HIV positivity or other acquired or congenital immunodeficiency disease; or a history of organ transplantation.
• Active or uncontrolled infection requiring systemic antibiotic therapy within 2 weeks before randomization or at the time of randomization.
• Active tuberculosis within 1 year or previous anti-tuberculosis treatment.

Other illness

• Unresolved postoperative complications at the time of randomization, such as postoperative infection, anastomotic leakage or wound dehiscence, gastrointestinal bleeding, pancreatic fistula, or intestinal obstruction.
• History of or current diagnosis of another malignancy within 5 years.
• Participation in another clinical study, or any condition that may interfere with the interpretation of the study results.
• Any other severe acute or chronic disease that, in the investigator's judgment, may increase the risk associated with study participation or study treatment.
• Diagnosis of interstitial pneumonia, noninfectious pneumonitis, pulmonary fibrosis, or acute lung disease.
• History of psychotropic drug abuse with inability to discontinue, or presence of a psychiatric disorder.

Other

• Presence of liver, peritoneal, or other distant metastases.
• Uncontrolled pericardial effusion, uncontrolled pleural effusion, or clinically significant moderate or greater ascites at screening, defined as any of the following: pleural effusion or ascites with clinical symptoms and detectable by physical examination; or pleural effusion or ascites requiring drainage and/or intracavitary treatment during screening.
• Female participants who are pregnant, breastfeeding, or planning to become pregnant during treatment or within 6 months after the end of treatment.
• Patients considered unsuitable for participation in this study by the investigator.

• Voluntarily signed written informed consent.
• Aged 18 to 75 years, inclusive, regardless of sex.
• Underwent radical gastrectomy with D2 or more extended lymphadenectomy and achieved R0 resection. Surgical approaches may include open or laparoscopic surgery.
• Histopathologically confirmed gastric or gastroesophageal junction adenocarcinoma.
• Received preoperative neoadjuvant immunotherapy combined with chemotherapy, including oxaliplatin plus fluoropyrimidine-based chemotherapy. Immunotherapy may include anti-PD-1 monoclonal antibodies, anti-PD-L1 monoclonal antibodies, PD-1/CTLA-4 bispecific antibodies, and other immune checkpoint inhibitors.
• Eligible for one of the following predefined cohorts:
  • Cohort 1: TRG grade 3 and postoperative pathological stage ypT3-4N2-3M0.
  • Cohort 2: TRG grade 0 and postoperative pathological stage ypT0N0M0.
• ECOG performance status of 0 or 1.
• No evidence of metastasis or recurrence on postoperative imaging before enrollment.
• Adequate organ function, defined as hematologic, hepatic, renal, and thyroid function meeting the protocol-specified criteria based on laboratory tests performed within 14 days before randomization.
• Willing and able to comply with the study treatment, scheduled visits, laboratory tests, and other study procedures.
• Female participants of childbearing potential must have a negative pregnancy test before enrollment and agree to use effective contraception during the study and for 6 months after the last dose of study treatment. Male participants with female partners of childbearing potential must agree to use effective contraception during the study and for 6 months after the last dose of study treatment.