Gastroscopy reports often see a description of a submucosal mass with a smooth surface, mostly less than 1 cm in diameter, in the fundus (gastric body or sinus), with ultrasound gastroscopy suggesting that the mass originates from the lamina propria and that a mesenchymal tumor may be considered. Usually, in this case, I would smile and tell the patient: “Don’t be nervous, it’s not a big problem”! So is it scary to encounter this situation or not? You will understand after we elaborate from several aspects. First of all, the morphological manifestation of this lesion under gastroscopy can be directly distinguished from what we often call gastric cancer, gastric lymphoma and gastric polyp, because it grows from the intrinsic muscular layer, while the previously mentioned diseases are all from the mucosal layer of the stomach, therefore, the mucosa of the submucosal mass is often the same as the normal tissue, except for individual cases that may appear to invade the mucosal layer. Second, the distinction between the mucosal layer and the intrinsic muscular layer depends on ultrasound gastroscopy, which is why many patients are advised to undergo ultrasound gastroscopy after general gastroscopy; third, the most common type of mass originating from the intrinsic muscular layer is gastric mesenchymal tumor, which accounts for 85-90% of all lesions, while the rest of the cases are seen in gastric smooth muscle tumors and other rare submucosal masses. Therefore, most of the masses suggested by ultrasound gastroscopy that originate from the intrinsic muscular layer are gastric mesenchymal tumors. 2. What is the incidence of small gastric mesenchymal tumors? Academically, mesenchymal tumors less than 2 cm in diameter are usually referred to as small mesenchymal tumors, so what is the incidence of small mesenchymal tumors in the stomach? We can only answer vaguely: “Very high, but specific data are not available”. For example, in a study from Japan, 50 small mesenchymal tumors were found in 35 of 100 surgical resection specimens of gastric cancer patients, which is a high enough rate. The reason why the specific data is not available is that most gastric mesenchymal tumors are asymptomatic and are often found incidentally during the examination of other diseases, so it is difficult to have detailed data on their incidence. 3. Are small mesenchymal tumors of gastric origin benign or malignant? Most small mesenchymal tumors are benign and will only grow very slowly during a person’s lifetime without causing any discomfort or endangering the patient’s life and health. However, there are very few small mesenchymal tumors that gradually appear as malignant tumors in the process of growth, showing rapid growth, combined with ulcers, bleeding, and even distant metastases at a later stage, which can be life-threatening. At this point, there must be some people who question: Don’t various academic monographs and the Chinese expert consensus on gastrointestinal mesenchymal tumors say that all mesenchymal tumors have malignant potential? Yes, this is the global consensus. In fact, the World Health Organization still classifies gastrointestinal mesenchymal tumors as benign or malignant, but the reason for this consensus is that we have not yet found a way to directly identify small mesenchymal tumors as benign or malignant, so for the time being, all gastrointestinal mesenchymal tumors are classified into four grades according to the risk of recurrence after surgery: very low risk of recurrence, low risk of recurrence, moderate risk of recurrence, and high risk of recurrence. This classification also reflects to some extent the malignancy of gastrointestinal mesenchymal tumors, in which those with very low risk of recurrence are almost benign. 4. Should small mesenchymal tumors be treated? In general, small mesenchymal tumors do not require treatment. The guideline recommendation is to review the gastroscopy regularly to observe the growth of small mesenchymal tumors, and if the growth is rapid, it indicates a certain malignant manifestation and needs to be removed surgically. One argument is that large mesenchymal tumors also grow gradually from small mesenchymal tumors, so small mesenchymal tumors should be actively operated on to kill them in the cradle. The only recommended treatment for small mesenchymal tumors is surgical resection. What types of small mesenchymal tumors require surgical treatment? Some small mesenchymal tumors with special manifestations and special locations need to be actively treated, including: gastroscopic findings of small mesenchymal tumors with mucosal ulceration or erosion; ultrasound gastroscopy findings of small mesenchymal tumors with uneven internal echogenicity and unclear borders, which often indicate poor biological behavior or certain malignant manifestations; small mesenchymal tumors growing adjacent to the cardia (the entrance of the stomach), which, if grown up, will face the risk of proximal gastric resection. The same applies to mesenchymal tumors adjacent to the duodenal papilla and rectal mesenchymal tumors adjacent to the anus. Therefore, the detection of small mesenchymal tumors by gastroscopy is not frightening, as their incidence is very high, and only a very small percentage of them develop progressive malignant changes, and regular gastroscopic review helps to determine the biological behavior of small mesenchymal tumors to decide whether further treatment is needed. Regular gastroscopic review can help determine the biological behavior of small mesenchymal tumors and determine whether further treatment is needed.