To clarify the efficacy and safety of endoscopic cryoablation combined with PD-1 monoclonal antibody treatment regimen in advanced gastric cancer.

This study is a single-center, single-arm, self-controlled, experimental, non-randomized exploratory clinical trial, aiming to enroll 15 patients with advanced gastric cancer. Each enrolled patient will be assigned a case number. This case number, along with the patient's name initials, will be recorded on every page of the case report form (CRF). Enrolled patients will receive local gastric ECAT (endoscopic cryoballoon ablation treatment) combined with PD-1 monoclonal antibody therapy for the evaluation of efficacy and safety, as well as immunological assessments of peripheral circulation and local tumor tissue. Patients will be followed during the treatment period and for six months after treatment termination for study observation.

Inclusion Criteria:

1. Patients diagnosed with advanced gastric cancer (stage IV in AJCC 8th edition staging, including locally progressive gastric cancer with unresectable factors (IVa) and gastric cancer with distant metastases (IVb); Bowman's staging type I, II, and III), who are unable to be surgically resected or do not tolerate surgical resection, and who have undergone progression after 1-2 lines of conventional chemotherapy;
2. Age greater than 18 years and less than 80 years;
3. WHO pathology type: adenocarcinoma, neuroendocrine tumor;
4. Expected survival greater than 3 months and controllable distant metastases as judged by the physician;
5. Important organ functions must be met: 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;
6. Blood routine: Hgb≥70g/L,ANC≥1.5×109/L,PLT≥80×109/L;
7. Coagulation function: PT and APPT <2 times the normal value;
8. Pregnancy test must be negative in women of childbearing age;
9. ECOG score ≤2;
10. Signed informed consent.

Exclusion Criteria:

1. Pregnant or breastfeeding women, or women with pregnancy plans within six months;
2. Infectious diseases (e.g. AIDS, syphilis, active tuberculosis);
3. Patients with active hepatitis B or C infection;
4. Combination of other primary malignant tumors;
5. Patients who have participated in a clinical trial within one month;
6. Patients taking antiplatelet or anticoagulant drugs within the last week;
7. Patients with gastric cancer combined with active bleeding;
8. Large amount of ascites (ascites ≥3000ml);
9. Cardia obstruction or pyloric obstruction;
10. patients with combined active infection or autoimmune disease;
11. Those who the doctor thinks there are other reasons not to be included in the treatment.