A Randomized Controlled Study of Endoscopic Cryoablation Combined With PD-1 Inhibitor for Maintenance Therapy in Advanced Gastric Cancer

Inclusion Criteria:

1. Patients diagnosed with advanced gastric cancer (stage IV according to the AJCC 8th edition, including locally advanced unresectable gastric cancer \[stage IVa\] and gastric cancer with distant metastasis \[stage IVb\]; Borrmann classification types I, II, or III) who are deemed ineligible for surgical resection or unable to tolerate surgery, and meet the indications for first-line therapy with sintilimab combined with fluoropyrimidine- and platinum-based chemotherapy;
2. Age ≥18 years;
3. WHO pathological types: adenocarcinoma or neuroendocrine tumors;
4. Physician-assessed estimated life expectancy greater than 3 months, with distant metastases considered controllable;
5. Maximum diameter of the primary tumor ≤6 cm;
6. Adequate major organ function, defined as:① Liver function: ALT and AST ≤ 2.5 times the positive range, total bilirubin ≤ 2.0mg/dL; ② Renal function: creatinine clearance ≥ 40mL/min calculated using the EPI formula;
7. Hematological criteria: hemoglobin (Hgb) ≥70 g/L; absolute neutrophil count (ANC) ≥1.5×10⁹/L; platelet count (PLT) ≥80×10⁹/L;
8. Coagulation function: prothrombin time (PT) and activated partial thromboplastin time (APTT) both \<2 times the normal value;
9. Negative pregnancy test for women of childbearing potential;
10. Eastern Cooperative Oncology Group (ECOG) performance status ≤2;
11. Signed informed consent form.

Exclusion Criteria:

1. Pregnant or breastfeeding women, or women planning to become pregnant within six months;
2. Patients with infectious diseases (such as HIV, syphilis, or active tuberculosis);
3. Patients with active hepatitis B or hepatitis C infection;
4. Patients with other concurrent primary malignancies;
5. Patients who have participated in another clinical trial within the past month;
6. Patients who have taken antiplatelet or anticoagulant medications within the past week;
7. Patients with gastric cancer complicated by active bleeding;
8. Patients with massive ascites (ascites volume ≥3000 mL);
9. Patients with cardia obstruction or pyloric obstruction;
10. Patients with active infections or autoimmune diseases;
11. Patients deemed unsuitable for treatment by the investigator for any other reason.