This project aims to collect peripheral blood samples from newly diagnosed gastric cancer patients and healthy individuals. Various techniques such as cfDNA sequencing, proteomics, and fragmentomics will be employed to analyze differences in the expression of ctDNA mutations, fragmentomics, and protein biomarkers between gastric cancer patients and healthy individuals. A new comprehensive diagnostic model will be established and its diagnostic value (sensitivity, specificity, accuracy, etc.) for gastric cancer will be validated.

Specifically, the study will involve the following subjects and quantities: 700 participants from Zhejiang Cancer Hospital (350 gastric cancer patients and 350 healthy individuals), 200 participants from Sichuan Cancer Hospital (100 gastric cancer patients and 100 healthy individuals), and 200 participants from the Sixth Affiliated Hospital of Sun Yat-sen University (100 gastric cancer patients and 100 healthy individuals). Peripheral blood samples (a total of 15mL from each participant, collected in 3 tubes) will be collected from all subjects. The collected blood samples will undergo multi-omics sequencing including cfDNA methylation sequencing, proteomics, and genomics to establish a multi-omics-based early diagnostic model.

Inclusion Criteria:

• Age between 18 and 100 years.
• ECOG performance status of 0 or 1.
• Pathologically confirmed Stage I-III gastric cancer patients.
• Patients who have not undergone any anti-tumor treatment (including chemotherapy, radiotherapy, targeted therapy, surgery, anesthesia, etc.) before blood collection.
• Subjects and their family members who can comprehend the research protocol and are willing to participate in the study, providing written informed consent.

Exclusion Criteria:

• Presence of other hereditary diseases or other tumors.
• Severe inflammatory reactions caused by acute illnesses within 14 days prior to blood draw or use of steroids.
• Previous organ transplantation, stem cell transplantation, bone marrow transplantation, or blood transfusion within the last month before enrollment.
• Pregnant women.
• Participation in other clinical trials requiring medication intake within the last 60 days (including anesthesia).
• Severe cardiovascular diseases, uncontrolled infections, or other uncontrollable comorbidities.
• Subjects or family members unable to comprehend the conditions and objectives of the study.

Number of Participants and Total Enrollment:

Zhejiang Cancer Hospital: 700/700 (350 cases of gastric cancer patients, 350 cases of healthy individuals) Sichuan Cancer Hospital: 200/200 (100 cases of gastric cancer patients, 100 cases of healthy individuals) The Sixth Affiliated Hospital of Sun Yat-sen University: 200/200 (100 cases of gastric cancer patients, 100 cases of healthy individuals)

This study does not involve clinical trials of drugs; it is solely designed to ensure the confidentiality of patient information. For participant information (such as names and ages), a coding system will be used instead of real names. After enrollment, each case will be assigned an enrollment number. Throughout the entire study, only the main researchers within the research team will have access to participants' real personal data (names, ages) in the electronic database. Distribution and sharing are prohibited. During the publication of articles, the main researchers within the research team will replace participant privacy information (names) with sample codes to achieve de-identification. Furthermore, the protection of participants' personal information will be maintained throughout the study, and any dissemination or leakage is strictly prohibited.