This was a case control, non-intervention study jointly developed by Fudan University Cancer Hospital and Shanghai Singlera Genomics Company. The enrolled population was screened by gastric surgery, including gastric cancer, precancerous lesions, benign lesions, and healthy control group. 10ml of whole blood of the enrolled subjects was collected for multi-target PCR detection of cfDNA methylation. The objective is to explore the clinical performance of polygene methylation (PCR-fluorescence probe) in the adjunctive diagnosis of gastric cancer, including the sensitivity of detection of various types and stages of gastric cancer, the specificity of detection of healthy controls, precancerous states, precancerous lesions, and the detection interference of other cancers. The diagnostic performance will be compared with CA199, CEA and CA724. The research data will provide a basis for screening targets for the development of detection kits.

Design and plan of the project: 1) Using the MONOD patent detection data of the company's previous research and combining with literature retrieval, analyze the tissue samples of gastric cancer of different stages and their paired paracancer tissues to screen the methylation mutation sites related to early gastric cancer and select the sites suitable for PCR detection; 2) ctDNA methylation markers in gastric cancer blood were preliminarily screened by plasma of healthy persons and preoperative plasma paired with tissues; 3) Using the screened blood ctDNA specific methylation markers, a targeted detection method for early gastric cancer lesions was designed; 4) The detection performance of the independent validation set sample confirmation establishment method.

Inclusion Criteria:

1. At least 18 years of age, no gender limitation;
2. those who can accept gastroscopy or provide pathological examination results of postoperative gastric biopsy
3. Patients newly diagnosed with stage I-IV gastric adenocarcinoma who had not received surgery, radiotherapy, chemotherapy, targeted therapy or other anti-tumor intervention before blood collection;
4. There were precancerous lesions and carcinoma in situ in the pathological examination of gastroscopy or esophageal biopsy, and no abnormalities in other gastric lesions, gastroscopy or other cancers. And no previous history of tumor disease.

Exclusion Criteria:

1. Previous digestive system tumors, including gastric cancer, esophageal cancer, colorectal cancer, liver cancer, etc.;
2. have a history of other cancers and have not been clinically cured (clinically cured: no recurrence and metastasis within 5 years after surgery);
3. Systemic inflammatory response syndrome;
4. A history of severe cardiovascular disease (e.g., previous myocardial infarction, coronary artery bypass grafting, or coronary stenting); A history of congestive heart failure; Patients with myocardial infarction within 6 months, uncontrolled severe hypertension, etc.) who were deemed unsuitable for inclusion by the investigator;
5. Those who have received major surgical treatment such as blood transfusion or transplantation within 3 months
6. Participants in other interventional clinical researchers, pregnant or lactating women, or patients with autoimmune diseases, genetic diseases, mental diseases, etc., within 3 months.
7. have participated in an "interventional" clinical trial within the past 30 days and have taken the experimental drug;
8. patients with other diseases deemed unsuitable for inclusion by the investigator;

Eligible participants were recruited from the Department of Gastrosurgery, Fudan University Cancer Hospital, including gastric cancer, precancerous lesions of gastric cancer, other gastric lesions, no abnormalities in gastroscopy, and other cancers.