After obtaining informed consent from the patients, all the medical history and treatment records of the patients who underwent gastroscopy since the onset of the disease, as well as gastric fluid samples, including laboratory and imaging data, were collected and recorded. The medical history and treatment records and gastric fluid samples were analyzed.

Inclusion Criteria:

• Patients underwent gastroscopy and treatment at the Endoscopy Center of Beijing Friendship Hospital, Capital Medical University, and received pathological biopsy.
• Previous gastroscopy suggested the possibility of lesions.
• No previous history of gastrointestinal cancer.

Exclusion Criteria:

• Patients could not cooperate with the examination or had contraindications to endoscopy.
• Previous history of gastrointestinal tumors, gastrointestinal surgery, physical and chemical injuries of the gastrointestinal tract.
• Severe bile reflux.
• Take simethicone and other defoaming agents before examination.
• Patients with serious diseases of heart, lung, kidney, brain, blood and other important organs.

Gastric cancer and non-cancer patients