(1) 18-75 years of age; (2) Meeting diagnostic criteria of CAG after upper gastrointestinal endoscopy; (3) Willing to cooperate with data, tissue sample, and blood sample collection during recruitment; (4) Willing to respond truthfully and timely to researcher queries after recruitment, able to cooperate with data, tissue sample and blood sample collection during follow-ups; (5) Willing to sign informed consent.