Disitamab Vedotin Combined With SOX Regimen Versus SOX Alone as Adjuvant Therapy for HER2-Moderate/High Expressing Stage Ⅲ Gastric Cancer: A Prospective, Multicenter, Randomized, Phase Ⅱ Clinical Trial

After providing informed consent and meeting all eligibility criteria, participants will begin adjuvant therapy with disitamab vedotin plus chemotherapy (SOX) approximately four weeks after surgery, continuing for 6-8 cycles. Post-operative imaging assessments will be performed every three months until disease recurrence. Following recurrence, survival follow-up will be conducted every three months. Safety visits will continue from first drug administration until 60 days after the last dose or until initiation of new anti-tumor therapy.

Inclusion criteria

• Aged between 18 and 75 years.
• Have undergone radical resection with D2 or wider lymph node dissection and achieved R0 resection status.
• No prior systemic anti-tumor treatment (i.e., neoadjuvant therapy) before surgery.
• Histopathologically confirmed gastric adenocarcinoma.
• Pathological stage III gastric and gastroesophageal junction adenocarcinoma patients (according to the 8th edition of the American Joint Committee on Cancer [AJCC] staging system).
• HER2 moderate-to-high expression (IHC 3+ or 2+).
• Eastern Cooperative Oncology Group Performance Status (ECOG PS) of 0 or 1.
• Expected survival time ≥ 3 months.
• Able to understand the study protocol, voluntarily participate in the study, and provide written informed consent;
• Good compliance and able to cooperate with the treatment regimen specified in this study;
• Possesses complete imaging and pathological clinical data;
• Adequate organ and bone-marrow function.

Exclusion criteria

• Primary stage III gastric or gastroesophageal-junction adenocarcinoma not histologically or cytologically confirmed;
• Unable to receive disitamab vedotin or SOX chemotherapy;
• Unable to comply with the required follow-up schedule;
• Unable to accept the treatment regimen specified in this protocol;
• Unable or unwilling to undergo mandated response assessments (e.g., CT imaging);
• Active autoimmune disease;
• History of psychoactive-substance abuse that cannot be discontinued, or any severe/uncontrolled psychiatric disorder, or any severe/uncontrolled systemic disease;
• Any concomitant condition that, in the investigator's opinion, poses significant risk to the subject or could compromise study completion;
• Other malignancies within 5 years before screening, except adequately treated cancers considered cured (e.g., thyroid cancer, cervical carcinoma in situ, basal/squamous-cell skin cancer, or ductal carcinoma in situ of the breast treated with curative surgery);
• Lactating women;
• Prior neoadjuvant therapy or intra-operative intraperitoneal chemotherapy.