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.