This is an observational study with a case control design. This study included patients with gastric cancer confirmed by pathological diagnosis of gastric tissue, and matched the control population according to age, gender, etc. In this study, researchers collected clinical information and multiple biological samples such as saliva, serum, and feces from the study subjects. We combined 16S rRNA sequencing and metabolomics to explore the differences in microbial and metabolic characteristics between gastric cardia cancer and non-cardia gastric cancer for early screening of gastric cancer.

Inclusion Criteria:

• Study population signing informed consent form
• Age: 18-75 years old
• The study population must underwent endoscopic examination and was confirmed by pathological diagnosis as gastric cancer: including high-level intraepithelial neoplasia, early gastric cancer, and advanced gastric cancer.

Exclusion Criteria:

• Those who have undergone gastrointestinal surgery within the past 1 year; Patients who have undergone neoadjuvant chemotherapy and have developed tumors in the residual stomach after previous partial gastrectomy.
• Those who have used proton pump inhibitors, antibiotics, probiotics, and prebiotics daily within the past month, and those who have recently received hormone therapy.
• People with infectious diseases and other digestive system diseases that interfere with the experimental results, such as inflammatory bowel disease, irritable bowel syndrome, etc.

Case:

The population in the case group signed an informed consent form, aged between 18 and 75 years. All subjects underwent endoscopic examination and were confirmed by pathological diagnosis as gastric cancer, including high-grade intraepithelial neoplasia, early gastric cancer, and advanced gastric cancer.

Control:

The age and gender of the study subjects in the control group were matched to the study population in the case group. The pathological results of the stomach of all subjects showed no malignant changes, including normal gastric mucosa, superficial gastritis, non atrophic gastritis, and gastric polyps, etc.