The main purpose of this study is to evaluate application value of OE mode 2 in the diagnosis of early gastric cancer The Secondary purpose is to evaluate application value of OE mode 1 in differentiating the diagnosis of neoplastic lesions of the gastric mucosa.

Gastric cancer is the most prevalent cancer in China，while the detection rate of early gastric cancer is lower than 10%. An effective screening method to improve the detection rate is urgently needed. Optical Enhancement (OE) mode is an endoscopic mode that uses the principle of grating for electronic staining, which provides a clear picture of the submucosal and superficial mucosal vascular structures. The OE1 mode provides enhanced images of the gastric Gland tube and blood vessels, as well as magnification. The OE2 mode is used to identify small chromatic aberrations and to visualize superficial structures in the gastric mucosa. So we designed this randomized controlled trial to discuss effectiveness of OE in the diagnosis of early gastric cancer and we hope to find an effective method to improve the detection rate of early gastric cancer in China.

Inclusion Criteria:

Meet item 1or 2 + any items of 3-7

1. Male ≥ 40 years old, female ≥ 50 years old.
2. More than one year since the last gastroscopy.
3. Patients from the areas with high incidence of stomach cancer (Shandong Province, Liaoning Province, Fujian Province, Gansu Province, Qinghai Province, Ningxia Province, Jilin Province, Jiangsu Province, Shanghai).
4. Patients with pre-cancerous gastric diseases such as chronic atrophic gastritis, gastric ulcer, gastric polyp, hypertrophic gastritis, pernicious anemia, etc. in the past.
5. First-degree relatives of patients with a family history of gastric cancer.
6. Other high-risk life factors for gastric cancer (high salt, pickled diet, smoking, heavy alcohol consumption, etc.)
7. Positive serum gastric function tests (GastroPanel) include: H. pylori (H.P) antibody （+）, Fasting pepsinogen I and II ratio (PG I/PGII) <3.89, gastrin 17 (G-17) >1.50 pmol/L.

Exclusion Criteria:

1. Patients who have undergone invasive treatment such as surgical resection, PEG, chemotherapy etc. of either stomach or oesophagus. (except for EMR and ESD).
2. Patients with a confirmed diagnosis of progressive cancer above T2 degreed according to the TMN classification of cancer。
3. Patients on anticoagulants that cannot be biopsied.
4. Patients who have undergone gastrectomy.
5. Patients who have taken PPIs or H2 receptor antagonist within two weeks.
6. Patients with history of malignant neoplasm; high suspicion of neoplasm; severe cardiac, pulmonary, hepatic or renal insufficiency; severe mental illness and pregnant women.
7. Patients who did not signed the consent form.