To facilitate the early gastric cancer diagnosis, an assay based on assessing large-scale methylation and fragmentation profiles of the plasma cell free (cfDNA) will be developed and validated.

Cancer-related features in cell-free DNA (cfDNA) fragments have gradually been identified and play essential roles for non-invasive early cancer detection. Integrated analysis of several cfDNA features have proven to achieve enhanced detection sensitivity as compared to single feature.

This study aims to develop and validate a novel blood-based whole methylome sequencing followed with a multi-dimensional model to analyze several features of cfDNA for GC early detection. Specifically, blood samples will be prospectively collected before gastroscopy. Cases and controls will be randomly divided into a training and a testing dataset at a ratio of 2:1. Plasma cfDNA will be isolated and extracted, followed with a bisulfite-free low-depth whole methylome sequencing. A multi-dimensional model named THorough Epigenetic Marker Integration Solution (THEMIS) including methylation, fragmentation, and chromosomal copy number alternation will be constructed in the training dataset. The performance of the model in differentiating cancer patients from non-cancer controls will then be evaluated in the testing dataset.

Inclusion Criteria:

1. Complete clinical info;
2. Patients self-agree to join the study and with signed patient consent and good compliance.

The specific inclusion criteria for subjects to be included in the malignant group:

1. According to the definition of AJCC's 8th Edition Cancer Staging Manual, patients with gastric adenocarcinoma confirmed by histopathology and with pathological stages of stage I-IV, including patients with esophageal gastric junction adenocarcinoma (EGJ);
2. Has not previously received any local or systematic anti-tumor treatment.

Exclusion Criteria:

1. Diagnosed previously with any kind of malignant tumor;
2. Have received total or partial gastrectomy;
3. Have received bone marrow or organ transplantation;
4. Have received blood transfusion in the past 6 months;
5. Incomplete clinical info or unqualified to participate in the study.

This study will enroll about 360 individuals who receive gastroscopy in The First Affiliated Hospital of Air Force Military Medical University (Xijing Hospital), Xi'an, Shaanxi province, China.

Two groups will be formed based on gastroscopy results, malignant group and non-malignant group. The malignant group includes patients diagnosed with high grade Intraepithelial neoplasia or GC (> 50% of patients in stage I and II) while the non-malignant group contains healthy individuals and patients with non-atrophic gastritis, gastric ulcer, gastric polyp or other benign gastric diseases.