Neuroendocrine neoplasms (NENs) are a very complex group of diseases – all endocrine cell-related tumors throughout the body can be included, so the disease can occur anywhere in the body and can metastasize to any site. Because most NENs are relatively inert, these tumors were named “carcinoid tumors” as early as 1907, and most of them are relatively inert, although a small number develop very rapidly. Most of them are relatively inert, but a few of them develop very rapidly. The most well-studied and most diverse tumors are gastroenteropancreatic neuroendocrine tumors, which are the subject of this topic. GEP-NENs mainly occur in the GI tract or pancreas and produce 5-hydroxytryptamine metabolites or peptide hormones such as glucagon, insulin, gastrin or adrenocorticotropic hormone. Tumors that secrete hormones that can cause clinical symptoms and syndromes are generally considered functional; tumors that have elevated levels of hormones such as pancreatic polypeptide (PP) detected in blood and urine without associated symptoms, or tumor compression that causes associated symptoms are considered non-functional, and most GEN- NENs are non-functional. NENs are non-functional. These diseases are unpredictable and heterogeneous, very different from other tumors, and even more distant from the common diseases of gastroenterology or endocrinology, and are in the middle gray area of multiple disciplines. In order to better understand the disease, its characteristics are summarized as follows: 1. Complex classification: NENs were first classified according to different origins in the embryonic period according to the anterior, middle and hindgut: the anterior intestine includes: lung, pancreas, stomach, duodenum, proximal jejunum; the midgut includes: distal jejunum, ileum, cecum, appendix; the hindgut includes: colorectum. According to different primary foci, GEP-NENs can be divided into pancreatic neuroendocrine neoplasms (pNENs) and gastrointestinal neuroendocrine neoplasms (GI-NENs). And GI-NENs are then named according to different sites of origin. Since tumors at different sites exhibit different characteristics, it is currently more recommended to classify them by specific primary sites. In addition, gastric NENs can be clinically classified into 4 subtypes: type 1 associated with type A atrophic gastritis, type 2 associated with gastrinoma/MEN-1, type 3 disseminated, and type 4 hypofractionated neuroendocrine carcinoma and mixed adenomatous neuroendocrine tumor (MANEC). type 1 and type 2 are both associated with hypergastrinemia, but type 1 patients present with gastric acid deficiency and atrophic gastritis, while type 2 presents with gastric acid hyperproduction of gastric acid. The 2010 version of pathological classification classifies NENs into G1/G2/G3 by Ki-67 and karyotype. G1/G2 are called neuroendocrine tumors (NETs), while G3 are called neuroendocrine cancers (NECs). It should be noted that grading is only a difference in cell proliferation activity and does not correspond exactly to its malignancy. Ki-67 is a clear prognostic factor for pNENs, but not for GI-NENs. Although there is still much controversy about the G1/G2 cut-off point, G1/G2 are relatively slow-growing overall, and there is no clear difference in treatment decisions. There are differences in the degree of differentiation among NECs, with poorly differentiated NECs having a similar degree of malignancy and survival as the corresponding cancer. There is no definite conclusion on how to treat the well-differentiated NECs, which are referred to as “highly proliferative NETs” in the 2013 China Pathology Consensus. The symptoms of GI-NENs are mainly carcinoid syndrome and related manifestations of type 1 and type 2 gastric NETs as described above. Functional pNETs can secrete many different hormones, commonly insulin and gastrin (see Table 1). Patients with insulinoma usually present with hypoglycemia, and functional pNETs also secrete hormones such as glucagon leading to diabetes mellitus and pro-adrenocorticotropic hormone leading to Cushing’s syndrome, and most of these patients are first seen in the endocrinology department; while for gastrinoma, patients are seen in the gastroenterology department for a long time due to elevated gastrin levels, leading to refractory stomach pain, diarrhea, and peptic ulcers. Therefore, if endocrinologists as well as gastroenterologists could have a deeper understanding of this disease, it would help more patients with functional, especially early, non-metastatic GEP-NENs to have an early and clear diagnosis and thus receive symptomatic treatment. 4. Special detection means and distinct imaging characteristics: The most sensitive and specific laboratory test is serum chromogranin A (CgA), which is mainly used to assist diagnosis and determine the efficacy and prognosis. In addition, CgB as well as NSE are optional tumor markers. For symptomatic patients, relevant hormone levels can also be measured. The common feature of these tests is that they are isotopically labeled on growth inhibitory receptors and have a higher sensitivity than the normal 18F-labeled PET-CT for well-differentiated NETs. Among them, 68Ga PET-CT is more sensitive and helps to detect more occult lesions. From this, we can see that GEP-NENs are extremely heterogeneous, and the first definite diagnosis requires the collaboration of several departments – endocrinology to identify the highly secreted hormones based on clinical manifestations and laboratory tests, gastroenterology to determine gastric acid secretion and endoscopy and biopsy, and oncology and imaging/nuclear medicine to identify the NETs by perfecting the orexin The oncology department and imaging/nuclear medicine department assist in the diagnosis and search for the primary site through specific examinations such as the orexin scan and 68Ga PET-CT. Surgical treatment has special principles for radical and palliative surgery and for the management of special complications before and after surgery, which are described in detail in the surgical treatment section. In addition, a significant proportion of GEP-NENs liver metastases have a very rich blood supply, making NENs liver metastases the most efficacious tumor for interventional treatment other than hepatocellular liver cancer. The treatments such as peptide receptor-mediated targeted radionuclide therapy (PRRT), for example, have been widely used abroad, and still need to be actively explored by nuclear medicine experts in China. In conclusion, one of the important reasons for the slow development of neuroendocrine tumors is that the mechanism of multidisciplinary discussion is not yet perfect, and doctors of various disciplines do not know enough about the disease. Therefore, a perfect multidisciplinary discussion can not only promote the most comprehensive and best treatment for patients, but also help to promote the knowledge and understanding of the disease among doctors, thus minimizing the misdiagnosis and misdiagnosis of the disease, so that patients with NENs can get the maximum benefit.