Eligible patients were randomized into two groups: the sodium propionate group and the control group. In the control group, patients received placebo combined with anti-PD-1 therapy plus chemotherapy without additional sodium propionate intervention. In the sodium propionate group, on the basis of anti-PD-1 therapy combined with chemotherapy, patients were additionally administered oral sodium propionate capsules at a dose of 500 mg (1 capsule) twice weekly, with a total intervention duration of 12 weeks. The primary and secondary outcome indicators will be collected for subsequent analysis.

Eligible patients with unresectable gastric cancer were randomly assigned to either the sodium propionate group or the control group. In the control group, patients received placebo combined with anti-PD-1 therapy and chemotherapy, without additional sodium propionate intervention. In the sodium propionate group, on the basis of anti-PD-1 therapy combined with chemotherapy, patients were additionally given oral sodium propionate capsules at a dose of 500 mg per capsule, one capsule twice a week, for a total intervention period of 12 weeks. Relevant primary and secondary outcome measures will be collected for further analysis.

Inclusion Criteria:

• Subjects voluntarily participated in the trial and signed the informed consent form;
• Aged ≥ 18 years and < 80 years, regardless of gender;
• Stable vital signs;
• Patients with gastric adenocarcinoma confirmed by gastroscopic biopsy;
• Tumors judged as unresectable by attending physicians;
• Receiving anti-PD-1 therapy combined with chemotherapy as first-line treatment;
• No history of allergic diseases and non-allergic constitution;
• No history of drug abuse;
• Non-pregnant and non-lactating females (applicable to male subjects as well);
• No participation in any drug clinical trial (including investigational drugs of this trial) within 3 months prior to enrollment.

Exclusion Criteria:

• Failure to meet the inclusion criteria, or individuals deemed inappropriate for trial participation by investigators;
• Concurrent primary malignant tumors at other sites;
• Poor general condition, severe infection, respiratory insufficiency, or other conditions leading to inability to cooperate with the trial;
• Patients with mental disorders, consciousness disturbance, or poor treatment compliance;
• Suspected or confirmed history of drug abuse;
• Immunodeficiency, or long-term use of immunosuppressants and glucocorticoids;
• Pregnant or lactating women;
• Sponsors, investigators directly involved in this trial, and their immediate family members;
• Individuals unsuitable for enrollment for any reason as judged by the investigator.