Laparoscopic Staging for Stage III Gastric Cancer

This study aims to compare, through a multicenter randomized controlled design, patients who undergo laparoscopic exploration staging before treatment (experimental group) with patients who receive treatment directly based on imaging findings (control group).Experimental Group: Will undergo laparoscopic exploration. If peritoneal metastasis (CY+ or P+) or cT4aN+ or cT4bN+ or M1 is found, recommendations include: Systemic therapy + NIPS ± HIPEC or HIPEC. If no metastasis is found, systemic neoadjuvant therapy is recommended.Control Group: Will not undergo laparoscopic exploration. Systemic therapy will be recommended directly based on imaging staging.

The primary objective of this study is to compare the 3-year overall survival (OS) between the two groups (experimental group and control group). Overall survival is defined as the time from randomization or start of treatment to death from any cause, with the 3-year survival rate serving as the primary endpoint to evaluate the long-term survival benefit of the two treatment strategies.

The secondary objectives of this study include the following three items:1.To evaluate the detection rate of peritoneal metastasis by laparoscopic staging (experimental group only).2.To evaluate the R0 resection rate after conversion surgery in both groups.3.To compare the surgical conversion rate (i.e., the proportion of patients who change from the original treatment plan to surgery) between the two groups.

Inclusion criteria

• Pathologically confirmed: Histologically proven adenocarcinoma of the stomach or gastroesophageal junction (Siewert type II/III).
• Definitive pathological markers: Documented status of HER2, MMR, CPS (PD-L1) score, and Claudin 18.2.
• Clinical stage: cT3/T4a N+ M0 based on contrast-enhanced CT, endoscopic ultrasound, or MRI (AJCC 8th edition):

cT3: Tumor invades through the muscularis propria into the subserosa. cT4a: Tumor penetrates the visceral peritoneum. cN+: Regional lymph node metastasis (intra-abdominal regional nodes such as perigastric, celiac, or common hepatic artery lymph nodes: short-axis diameter > 8 mm; other nodes such as retroperitoneal or para-aortic lymph nodes: short-axis diameter > 10 mm).

No evidence of peritoneal metastasis on imaging modalities other than laparoscopic exploration.

• Age: 18 to 75 years, regardless of sex.
• Performance status: ECOG score 0-2 (fully active to ambulatory and capable of self-care but unable to work).
• Life expectancy: Estimated survival ≥ 6 months.
• Surgical fitness: Adequate cardiopulmonary functional reserve and no contraindications to anesthesia.
• Informed consent: Voluntary participation with written informed consent obtained.

Exclusion criteria

• 1. **Gastric outlet obstruction:** Requiring gastrojejunostomy due to obstructive symptoms.

• **Distant metastasis:** Evidence of peritoneal, mesenteric, or omental metastasis and/or obvious ascites on imaging, or distant organ metastasis.

• **Other malignancies:** History of or concurrent other malignant tumors (except curatively treated basal cell carcinoma of the skin).

• **Organ dysfunction:** Severe cardiac insufficiency (NYHA class III-IV), hepatic dysfunction Child-Pugh class C, or creatinine clearance < 30 mL/min.

• **Contraindications to laparoscopy:** History of severe intra-abdominal adhesions, coagulation disorders (INR > 1.5 or platelet count < 50 × 10⁹/L), or severe intestinal obstruction.

• **Special populations:** Pregnant or lactating women, or those unable to interrupt breastfeeding.

• **Mental status:** Cognitive impairment or psychiatric disorders that preclude compliance with follow-up.