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

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.