Since the digestive tract is responsible for the body’s function of digesting and absorbing food, it is also susceptible to tumors in contact with external environmental harmful substances. Among human tumors, the proportion of tumors in the digestive tract (esophagus, stomach, small intestine, large intestine and rectum) is the highest. With the development of modern medical technology, most benign tumors, even malignant tumors without metastasis and with shallow mucosal infiltration depth (early stage cancer), can be removed through gastrointestinal endoscopy in a non-invasive way, avoiding open or laparoscopic surgical treatment and greatly improving the quality of life. As we know, the so-called tumor is an extra piece of uncontrolled growing tissue, usually protruding from the mucosal surface of the digestive tract, and benign tumors are called polyps. The general endoscopic minimally invasive treatment of GI tumors refers to these polyps protruding from the mucosal surface of the GI tract, which can be removed by endoscopic means with a trap, the tip underneath the polyp, and then by electrocoagulation cutting. Even huge polyps, that have only a very short tip (), can be removed with a captive device. This method, however, is powerless for those tumors (polyps) without a tip, that is, those growing against the mucosal surface, because it is impossible to de-capsule them. Therefore, for these flat (flat, or flat and concave) tumors with smaller diameters, endoscopic mucosal resection (EMR) is used. The human digestive tract can be simply divided into three layers, namely the mucosal layer, the submucosal layer, and the outer muscular layer (which is a bit more complicated medically and will not be described in detail). The mucosal layer is the innermost layer of the intestine, and epithelial tumors of the digestive tract (malignant tumors are “cancer”) all originate from the mucosal layer. If a flat tumor grows on the mucosal surface, liquid can be injected into the submucosal layer to form a liquid cushion, which will elevate the tumor in the mucosal layer, and then the tumor can be removed with a trap, i.e., EMR. For large diameter flat tumors, the EMR method can be used multiple times, which is called the EPMR method. However, there are obviously some problems with the EMR method, that is, for larger flat tumors, it is difficult to remove them all at once. Moreover, when doing EMR, you do not know some conditions under the mucosa, such as how thick the blood vessels are and whether there are adhesions between the mucosa and the submucosa, so the potential danger is high. For flat tumors with fibrous adhesions between the mucosa and submucosa, EMR is not able to do anything. Therefore, based on this, endoscopic submucosal dissection (ESD) was invented. ESD also involves the injection of fluid into the submucosa to form a fluid pad that separates the mucosa from the submucosa (see Figure 1). The difference is that ESD first uses an electric knife to completely dissect the mucosal layer around the tumor to reveal the submucosal layer. In order to clearly show whether it is the submucosa or not, a stain called indigo carmine is added to the fluid injected by ESD, which can stain the submucosa, so that the submucosa can be shown without cutting through the head. After the mucosal layer was cut open to reveal the submucosa, the submucosa was slowly peeled off with a knife. Since the submucosa is mainly loose connective tissue and blood vessels, the mucosa (apple skin) can be peeled off under endoscopic surveillance, just like peeling an apple. This process allows for effective or prophylactic hemostasis and appropriate peeling and cutting to avoid hemorrhage or perforation, as the blood vessels and fibrotic adherent tissue can be clearly seen. However, it must be noted that, despite this, ESD is a difficult and high-risk intervention that can have serious complications, such as bleeding, perforation and post-treatment stricture of the digestive tract, which can be life-threatening in severe cases, as with other interventional or surgical treatments. Currently, ESD technique is considered to be an effective treatment for early-stage mucosal tumors of the esophagus, stomach and intestine, especially for those flat tumors (early-stage esophageal, gastric, colon and polyps), or those large polyps that are difficult to be removed by conventional methods. Polyps that have been treated with EMR or EPMR techniques can also be treated with ESD when they recur due to fibrosis in the lesion area, which then adheres the mucosal and submucosal layers. Japan is a country with a high incidence of gastric cancer, and they have used this technique for the treatment of early gastric cancer with very good results. Because of the technical difficulty and time-consuming operation of ESD and the high technical requirements of the operator, this technique is not commonly performed in China at present. We have carried out this technique after learning ESD technique from Japan (Attachment 2). Our experience has shown that ESD can significantly improve the quality of life of patients and shorten the length of hospital stay compared with open surgery or laparoscopic surgery. Figure 1: Schematic diagram showing ESD treatment of flat tumors (early stage cancer), in which the green area represents the diseased tumor and the blue area represents the fluid injected into the submucosa to form a fluid pad during ESD. Figure 2: Our first ESD procedure for a patient with lateralized developmental tumor (LST) of the sigmoid colon. a: LST of the sigmoid colon seen under conventional endoscopic white light; b: LST seen by narrow band imaging (NBI) with more clearly identifiable lesion margins; c: lesion extent marked by endoscopic APC first; d: lesion circumferential resection; e: mucosal peeling in endoscopy; f: LST lesion was completely resected.