Pathological evidence is needed to confirm the diagnosis of gastric cancer, and to obtain pathological evidence of gastric cancer, it is often necessary to obtain tissue through gastroscopic biopsy and observe it under a microscope to determine the diagnosis. If a lump is found on the left side of the patient’s neck, which is suspected to be caused by metastasis of gastric cancer, it can be surgically removed, or tissue can be obtained through fine needle aspiration for laboratory examination. Gastroscopy and barium meal examination are the common methods to diagnose gastric cancer, which will be described in detail below. Gastroscopy is to put a special tube into the stomach through the mouth, which can directly observe whether there is any abnormality in the stomach. Barium meal is to drink a white contrast agent to indirectly reflect abnormalities in the stomach, and also to see the size, shape and peristalsis of the stomach, but unlike gastroscopy, a special grasping forceps can be put in through the tube to grasp the tissue for pathological examination. Many people believe that gastroscopy can replace other examinations by directly observing the morphology and color of the gastric cavity and also biopsying the gastric mucosal tissue. In fact, gastroscopy cannot observe the adjacent tissues of the stomach, and it is easy to miss the diagnosis of lesions with insignificant destruction of the gastric mucosa and predominantly submucosal infiltration. In our clinical practice, we have also encountered cases in which the diagnosis could not be confirmed even after five biopsies of gastroscopy, including excisional biopsy, but the upper gastrointestinal tract imaging showed that the gastric cancer was very typical and the surgery also confirmed that it was gastric cancer. The method of upper gastrointestinal barium meal imaging is simple and only requires preparation on an empty stomach, which is generally acceptable to patients, especially for young or old and weak patients. 1.Gastroscopy Gastroscopy is a special tube placed into the stomach cavity from the mouth through the esophagus to directly observe the changes of gastric mucosa in various parts, such as congestion, edema, atrophy, ulcer, bleeding, inflammation and tumor. When gastroscopy finds suspicious lesions in esophagus, stomach or duodenum, the biopsy forceps at the front of gastroscope can be used to take biopsies for pathological examination, so as to determine the nature of lesions, detect early gastric cancer in time and prevent leakage and misdiagnosis. Patients with chronic ulcer disease, especially those over 40 years old, should be alerted when they have unexplained wasting and anemia, and regular gastroscopy can be helpful for early diagnosis. Gastroscopy is sometimes associated with complications, the more serious of which are cardiopulmonary accidents, severe bleeding, and perforation. Infection is a less common complication, mainly aspiration pneumonia, which manifests as fever, cough, chest tightness and shortness of breath. The irritation in the pharynx and bloating in the abdomen during gastroscopy will inevitably discourage some patients. It is also not suitable for patients with serious conditions, such as hemorrhage, shock, bad heart, coma, and those who are too old and weak to cooperate. However, many hospitals are now performing gastroscopy under anesthesia, which can very well reduce or even eliminate the pain of patients. Gastroscopy has a high level of safety, and due to the strict cleaning and disinfection process, it generally does not cause mutual transmission of diseases among patients. At present, hospitals mostly require the presentation of infection screening results before gastroscopy, and patients with infectious diseases need specific examination and disinfection measures. 2.Barium X-ray examination Barium X-ray examination is performed by drinking barium that is impervious to X-rays and allowing it to coat the surface of the gastric mucosa. The area where the barium goes can be shown more clearly by taking a film, and while observing the morphology of the esophagus and stomach, it can indirectly reflect whether there are lesions in the gastric mucosa. When there is a tumor present, the image of filling defect can appear where the barium is covered. For patients with epigastric pain, fullness or choking sensation when eating, as well as pain or burning sensation behind the sternum, barium X-ray examination should be considered. The above methods are mainly to determine the diagnosis of gastric cancer, but in a broad sense, after the diagnosis of gastric cancer is determined, there is another issue of staging diagnosis. Staging diagnosis simply means whether the disease is in early, middle or late stage. The treatment of gastric cancer is also determined based on the stage of gastric cancer, and the treatment methods for early, middle and late stage are different, and the treatment effects are also different. In the following, the staging of gastric cancer and how to perform staging examination will be briefly introduced.