The mass is primarily in the stomach, but can also be found in the esophagus, small intestine, and large intestine. It is called a submucosal swelling to distinguish it from a mucosal swelling. Most lesions seen on gastroscopy are lesions of the mucosa, such as inflammation, atrophy, enterosis, intraepithelial neoplasia, and even cancer. These lesions are either breaks in the mucosa or hyperplasia or even malignant proliferation. One has the most mucosal lesions, after all, it is located in the innermost part of the gastric cavity, which is in direct contact with food and foreign substances, so it is most likely to have lesions; the other can be directly observed by the gastroscopy lens because it is located on the surface of the cavity. However, there are some lesions where the mucosa on the surface is intact, although the gastroscope can see a clear bulge, or although it has caused damage to the mucosa, an experienced endoscopist can see that the origin of the lesion is not the mucosa. These masses are also tumors, and since they are tumors there are benign and malignant, but the malignant ones are not called cancer, but sarcoma. This is determined by the naming rules of tumors. The so-called cancer pathology refers only to malignant tumors from epithelial tissue. In other words, these submucosal tumors are from non-epithelial tissues. Within the organ, epithelial cells are generally classified as parenchymal and non-epithelial cells as mesenchymal. Therefore, these tumors are collectively referred to as mesenchymal tumors. Because of the mixed cellular composition of origin, the benignity and malignancy of different mesenchymal tumors vary greatly. Some mesenchymal tumors may go undetected for a lifetime unless they are discovered by gastroscopy or surgery for an unrelated condition. It has been reported that small gastrointestinal mesenchymal tumors can be found in more than twenty percent of autopsies. Some are highly malignant and grow rapidly, presenting symptoms such as intestinal obstruction, bleeding, and metastasis to organs such as the liver through blood flow. Since mesenchymal tumors have the possibility of malignancy, it seems that they should be treated like other gastric tumors: biopsy first, pathological diagnosis to identify benign and malignant, no treatment or follow-up for benign, surgical resection for malignant, and then chemotherapy. However, gastroscopic biopsy has an inherent defect: insufficient depth. Biopsy forceps are designed to collect mucosal samples, so it is difficult to dig into the submucosal tissues and occasionally take a little bit to reflect the whole picture of the tumor. In contrast, determination of the malignancy of mesenchymal tumors requires a combination of three indicators: tumor diameter, site, and nuclear division index. The last one is crucial, but requires observation of at least 50 high-powered views. In contrast, in addition to the difficulty of obtaining biopsies, another important drawback of ordinary endoscopic diagnosis is the inaccurate judgment of tumor diameter. Because mesenchymal tumors are located in the submucosa, what can be observed by ordinary gastroscopy is only the small part that protrudes from the mucosal surface, so the diameter of the tumor is usually underestimated. This requires the use of one of the sharpest tools of gastrointestinal endoscopy: ultrasound endoscopy. The principle of ultrasound endoscopy is similar to that of body surface ultrasound, except that the ultrasound probe is mounted on the end of the internal lens, which reaches the lumen with the help of the endoscope and makes contact with the mucosa to obtain a cross-sectional image of the entire wall of the digestive tract and the surrounding organs. In the case of mesenchymal tumors, the ultrasound endoscope not only accurately measures the diameter of the tumor, but is also able to determine exactly where the tumor is located in the wall of the canal. With the help of ultrasound Doppler, it is also possible to evaluate the blood flow within and around the tumor. Experienced ultrasound endoscopists can also predict the type of tumor based on morphology and echogenicity. Ultrasound endoscopy has basically become a routine examination tool for mesenchymal tumors, but it also has blind spots and dead ends for observation, and requires a high level of operator, so it has not yet become a popular device in all hospitals. In recent years, domestic gastroenterology clinicians have been paying more and more attention to mesenchymal tumors, based on the popularity of endoscopy, which has led to more and more people being detected, and the facilitating factor is the development of endoscopic treatment, especially the development of endoscopic mucosal resection and peeling techniques. For the diagnosis and treatment of a disease, it is generally considered to detect the disease and improve the diagnosis before considering the treatment. However, in places like China, where innovation is lacking and imitation is superb, it is often the other way around. Because diagnosis is mostly worthless, treatment is always a little more, although it doesn’t make much money either. When a new treatment technology is recognized abroad, it is introduced and carried out in China in order to increase the number and promote doctors to open their eyes to discover more cases. The pursuit of quality after reaching a certain number requires a good grasp of indications, and so in turn requires an improved level of differential diagnosis. For the endoscopic treatment of submucosal masses, we are currently in such a transitional stage from quantity to quality. As for the extent of the transition, it varies from region to region and from hospital to hospital. Given the unreliability of general endoscopic diagnosis, if all cases are taken out, many are bound to be overtreated. However, if all of them are ignored, there are bound to be delays. Most of the clinical knowledge of mesenchymal tumors is still at the stage of case summary, which is retrospective information and lacks systematic and comprehensive evidence-based medical evaluation to predict the natural outcome of newly discovered cases. What is available is only expert consensus opinion. In general, the evaluation is still based on a combination of three indicators: site, diameter and nuclear division, and the risk level is divided into five levels: none, very low, low, medium and high. If it is in the stomach, the nuclear fission index is the first boundary, less than or equal to 5, only if the diameter is greater than 10 cm is it considered to be intermediate risk, if the nuclear fission index is greater than 5, a diameter greater than 2 cm is considered intermediate risk, and greater than 5 cm is considered high risk. The duodenum and rectum are rated higher, as long as the diameter is greater than 10 cm, regardless of the nuclear split, all are considered high risk; if the nuclear split index is greater than 5, also regardless of the diameter, all are considered high risk. The problem is that this expert consensus is for post-surgical patients and does not apply to patients with endoscopic findings. The question for both the physician and the patient is whether or not the lesion, which is detected by endoscopy and measured by ultrasound endoscopy, needs to be removed endoscopically. Because most of the lesions are in the stomach, also using the example of gastric mesenchymal tumors, it is assumed that treatment is required for intermediate risk, with an unknown term for the nuclear splitting index. If the nuclear fission index is less than or equal to 5, it would have to be greater than 10 cm in diameter to be treated, which is well beyond the limits of endoscopic manipulation, and the patient is faced with a surgical gastrectomy. Assuming that the nuclear division index is greater than 5, then a diameter greater than 2 cm would be of therapeutic value. In contrast, gastric mesenchymal tumors below 2 cm are considered risk-free regardless of any nuclear division. Obviously, it becomes crucial to predict nuclear division in mesenchymal tumors larger than 2 cm in diameter without removing the tumor. Unfortunately, such a method does not yet exist. The only noninvasive technique capable of fully visualizing the morphology of mesenchymal tumors, ultrasound endoscopy, has many observations, but they are all subjective in nature and are poorly consistent with pathologic histology. Although some people have tried to diagnose with ultrasound endoscopy-guided fine needle aspiration, that is only for larger tumors and the lack of accuracy is also problematic. Many of the submucosal masses found today are very small, many less than a centimeter or so in diameter. For such lesions, going for endoscopic resection is bound to be overtreatment in many cases. However, it is important to emphasize that mesenchymal tumors are still poorly understood. The sudden increase in clinical cases is only in the last decade or so, and norms for the endoscopic treatment of smaller mesenchymal tumors are not yet available. The treatment probably requires full communication and joint decision between the physician and the patient, especially the physician should refrain from exaggerating the risks.