The primary purpose of this trial is to describe the profile of ctDNA methylation in gastric cancer. The second purpose is to demonstrate the correlation between the plasma ctDNA methylation status and the diagnosis and prognosis of patients with early and intermediate stage gastric cancer.

Gastric cancer represents one of the common malignant tumors in China, with high incidence and mortality rates. Surgery is the conventional treatment option for early and intermediate stage gastric cancer, but the diagnosis in the early stage of gastric cancer remains a challenge to clinical practitioners. Circulating tumor DNA (ctDNA) is tumor-derived fragmented DNA with an average size of 166 bp, mixed with cell-free DNA (cfDNA) of other sources in blood circulation. ctDNA is reflecting the most up-to-date status of the tumor genome. Hence, it is considered as a novel biomarker for tumors, which can be qualitative, quantitative, and used for disease monitoring. This study is designed to evaluate the potential clinical utility of circulating tumor DNA (ctDNA) as a clinical index in the diagnosis and prognosis of gastric cancer. The primary purpose of this trial is to describe the profile of ctDNA methylation in gastric cancer. The second purpose is to demonstrate the correlation between the plasma ctDNA methylation status and the diagnosis and prognosis of patients with early and intermediate stage gastric cancer.

Inclusion Criteria:

1. The subject is scheduled to undergo an endoscopy because of medical indications.
2. The subject must have personally signed and dated the patient informed consent form indicating that he/she has been informed of all pertinent aspects of the study.
3. The subject must be willing and able to comply with all study procedures.

Exclusion Criteria:

1. The subject who is unable to undergo gastroscopy.
2. The subject with previous total or partial gastrectomy.
3. The subject has other severe acute or chronic medical or psychiatric condition or laboratory abnormality that may interfere with the interpretation of study results and in the judgment of the investigator would make the subject unsuitable for entry into the study.
4. The subject is unwilling or unable to provide signed informed consent.
5. The subject who is pregnant.

Patients who have been referred to the participating study sites for upper GI endoscopy for standard clinical indications.