The goal of this multicenter, randomized, phase III clinical trial is to test whether robot-assisted radical gastrectomy improves 3-year recurrence-free survival versus laparoscopy-assisted radical gastrectomy in adults aged 18-80 years with previously untreated, resectable cT4a gastric adenocarcinoma and non-bulky lymph nodes; the main questions are whether the robotic approach confers superior RFS and maintains equivalent peri-operative safety (Clavien-Dindo ≥ II complications) and better secondary oncologic outcomes, and participants will be randomized 1:1 to undergo standardized D2 resection via robotic or laparoscopic technique and followed for 5 years with scheduled recurrence, survival, and quality-of-life assessments.

Inclusion Criteria:

Histologically confirmed gastric or Siewert type III (and selected type II) gastro-oesophageal junction adenocarcinoma, clinical stage cT4a without bulky lymph-node enlargement on contrast-enhanced CT or MRI No prior neoadjuvant chemotherapy, radiotherapy, or other anti-cancer therapy Tumour deemed amenable to R0 resection by a board-certified gastric surgeon and radiologist ECOG performance status 0-1 Estimated life expectancy ≥ 6 months

Adequate organ function defined by:

• ANC ≥ 1.2 × 10⁹/L, platelet ≥ 100 × 10⁹/L, Hb > 8 g/dL (no transfusion/G-CSF within 14 days)
• ALT/AST ≤ 2.5 × ULN, total bilirubin ≤ 1.5 × ULN (or isolated indirect hyperbilirubinaemia)
• Serum creatinine ≤ 1.5 × ULN and calculated creatinine clearance ≥ 60 mL/min
• INR or PT ≤ 1.5 × ULN (therapeutic low-dose anticoagulation allowed)
• TSH and free T4 within normal limits or clinically insignificant deviation BMI ≥ 18.5 kg/m² or body weight ≥ 40 kg Signed informed consent

Exclusion Criteria:

cT4b disease, distant metastasis, or peritoneal cytology positive for malignancy Bulky lymph-node conglomerates (> 3 cm short axis) or N3 disease precluding D2 dissection Previous gastrectomy or major upper-abdominal surgery (except uncomplicated laparoscopic cholecystectomy) within 5 years Concurrent malignancy within 5 years (except adequately treated basal-cell carcinoma, carcinoma in situ, or stage I tumours) Gastric cancer arising from emergency presentation (bleeding, perforation, obstruction) Planned multi-visceral resection for non-oncologic indication Active bleeding diathesis; INR > 1.5 off anticoagulants; history of grade ≥ 3 bleeding within 4 weeks Arterial or venous thrombo-embolic event within 6 months Clinically significant cardiovascular disease: NYHA class III-IV heart failure, LVEF < 50 %, myocardial infarction or unstable arrhythmia within 6 months, QTc ≥ 450 ms (men) or ≥ 470 ms (women) Severe chronic pulmonary disease: FEV₁ < 50 % predicted or oxygen-dependent Uncontrolled diabetes (HbA1c > 8 %), active autoimmune disease requiring systemic immunosuppression, or corticosteroids > 10 mg/day prednisone equivalent within 14 days Active infection requiring systemic antibiotics, HIV, hepatitis B (HBV DNA ≥ 500 copies/mL), hepatitis C, or tuberculosis Pregnancy, lactation, or fertile participants unwilling to use effective contraception Psychological disorder, substance abuse, or any condition that, in the investigator's opinion, would compromise protocol compliance or safety