The study is a prospective cohort study to investigate whether aberrant DNA methylation can be useful for the prediction of metachronous recurrence after endoscopic resection of gastric neoplasms (dysplasia or cancer). From 2012 to 2017, 300 patients were prospectively enrolled after endoscopic resection (ER) of gastric dysplasia or early gastric cancer. All lesions were assessed by endoscopy and biopsy before ER. Endoscopic mucosal resection (EMR) or endoscopic submucosal dissection (ESD) was performed for gastric dysplasia and early gastric cancers which met the absolute indication (differentiated adenocarcinoma, intramucosal cancer, lesions < 20 mm, and no endoscopic evidence of ulceration). All lesions were curatively resected; if non-curatively resected, the patients were not enrolled from the study. All subjects, who provided informed consent, were asked to complete a questionnaire under the supervision of a well-trained interviewer. The questionnaire included questions regarding demographic data (age, sex), socioeconomic data (smoking, alcohol, and education), their family history of GC in first-degree relatives, and history of H. pylori eradication therapy. Also, MOS methylation level at baseline was measured from noncancerous gastric mucosae at corpus. When H. pylori was positive by CLOtest or histology at baseline or during the follow-up, eradication therapy was done. To evaluate whether H. pylori was eradicated, 13C-urea breath testing was performed at least 4 weeks after completion of the eradication therapy. All study subjects were closely followed up since recurrent tumors at previous endoscopic resection sites can be easily detected on endoscopy with biopsy and treated during follow-up. Patients with local recurrence underwent further treatments, including repeated ESD, APC, and gastrectomy based on pathology, and patients who refused treatment received supportive care. All patients underwent endoscopy with biopsy within 6 months, then at 12 months after ESD to check for metachronous lesions or local recurrences. After 12 months, endoscopy with biopsy was performed annually. In case of EGCs, abdominal CT scan was performed in the first year and biennially thereafter to detect lymph node or distant metastases. The definition of the completion of the study protocol was 1) endoscopic and/or radiologic follow-up for more than 3 years, or 2) development of metachronous gastric neoplasm (primary outcome: gastric dysplasia or cancer) during the follow-up. Metachronous recurrence was defined as secondary dysplasia or cancers detected > 1 year after initial diagnosis.

Inclusion Criteria:

• Patients who underwent endoscopic resection of gastric neoplasms (dysplasia or early gastric cancer)
• All gastric neoplasms at diagnosis should be curatively resected before enrollment.

Exclusion Criteria:

• Previous history of all cancers.
• Previous history of gastrectomy
• Non-curative resection of gastric neoplasms
• Refusal to consent

Patients with gastric neoplasms (gastric dysplasia or early gastric cancer) which was curatively resected endoscopically.