A Clinical Study Evaluating the Efficacy of Systemic Chemotherapy and Immune Checkpoint Inhibitors Combined With Hyperthermic Intraperitoneal Chemotherapy in the Treatment of Gastric Cancer Patients With Peritoneal Metastasis

Inclusion Criteria: 1. 18-75 years 2. Men, or non-pregnant and non-lactating women 3. Pathological diagnosis as gastric malignant tumor 4. diagnosis of peritoneal metastasis \[peritoneal cancer index (PCI) ≤ 12 points\] by laparoscopic exploration 5. Normal major organ function: 1\) HB ≥ 90 g/L； ANC ≥ 1.5×109/L; plt ≥125×109/L; 2) TBIL\<1.5ULN; ALT, AST \<2.5ULN; Cr≤1.25ULN; ALB ≥ 30 g/L 6. Not receive radiation therapy, chemotherapy, targeted therapy, or immunotherapy. 7\. Eastern Cooperative Oncology Group Performance Status (ECOG): 0-1 8. Patients are volunteers, have signed informed consent, and agree to cooperate with investigators in data collection. Exclusion Criteria: 1. Patients have other malignant tumors within the past 5 years. 2. Patients use immunosuppressant within 30 days prior to the initial use of tirelizumab, excluding nasal sprays and physiological doses of inhaled corticosteroids or systemic steroids from consideration. 3. Patients have a documented history of ongoing autoimmune conditions or prior autoimmune diseases. 4. Patients are allergic to oxaliplatin, S-1, other related chemotherapy drugs or immune checkpoint inhibitors. 5. Patients with epilepsy or other mental disorders. 6. Patients who are unable to undergo surgery due to severe heart, lung and vascular diseases. 7. Pregnant or lactating women. 8. Patients with other distant metastasis