Neuroendocrine tumors (NETs) are a group of tumors that originate from neural and endocrine cells in the body. Neuroendocrine cells are widely distributed throughout the body including pituitary, thyroid, parathyroid, lung and thymus, gastrointestinal tract, pancreas, adrenal glands, skin and other organs and tissues. Therefore, neuroendocrine tumors can occur in any of these organs and tissues. What is a functional neuroendocrine tumor? Neuroendocrine tumors can produce and secrete common hormones, and NET patients may or may not have hormone-related clinical symptoms. The most common sites of NETs are the pancreas, gastrointestinal tract, lungs and thymus. What is the incidence of neuroendocrine tumors? Neuroendocrine tumors are rare diseases, but their incidence has been increasing over the past 30 years, with an incidence rate of 5.25 per 100,000 in 2004 in the U.S. NETs are difficult to detect early, and more than half of patients have metastases by the time they are diagnosed. Unlike common cancers, most NETs grow slowly, with lymph nodes and the liver being the most common sites of metastasis. When should neuroendocrine tumors be suspected? Patients with neuroendocrine tumors of gastrointestinal origin may present with carcinoid syndrome: flushing of the skin, diarrhea, abdominal pain, wheezing, and heart valve lesions. Not all of these manifestations may be present. When patients have diarrhea and abdominal pain that persist for a long time, it is important to think if these symptoms are caused by NET and a blood CgA test can be performed. When the patient has paroxysmal skin flushing, it should be differentiated from menopausal syndrome, and at the same time, it should be suspected whether there is NET, and NET-related tests should be performed. Functional neuroendocrine tumors of the pancreas include gastrinoma, insulinoma, glucagonoma, and VIP tumor, which are each associated with characteristic hormonal syndromes. When patients with these rare tumors seek medical attention, physicians with NET expertise are generally less likely to misdiagnose them and can perform relevant hormone level tests (e.g. gastrin, insulin, glucagon) to aid in the diagnosis. How to diagnose neuroendocrine tumors? The biochemical markers of neuroendocrine tumors – serum CgA, serum NSE and urinary 5-HIAA tests – can be done for all patients with suspected NET. If a functional pancreatic NET is suspected, blood can be drawn for appropriate hormone testing. Growth inhibitory receptor imaging (octreotide scan) is a whole-body nuclear medicine test for neuroendocrine tumors and can be used to detect primary and metastatic lesions with a sensitivity of about 80%. Suspected gastrointestinal NET usually requires gastroscopy, colonoscopy or small bowel microscopy to find the primary lesion and perform biopsy. The diagnosis of NET ultimately relies on biopsy specimens or surgical specimens for pathological confirmation. Because neuroendocrine tumors are relatively rare, pathology reports should be confirmed by consultation with a pathologist with expertise and interest in NET. What is the treatment and prognosis of neuroendocrine tumors? The treatment of neuroendocrine tumors of different types and locations is quite complex and varied, and requires guidance from a NET specialist. Early-stage NETs are usually curable with surgical or endoscopic resection. The prognosis of NET patients is related to the clinical stage and pathological grading of the tumor. (The same stage) Patients with low-differentiated, high-grade neuroendocrine carcinoma have shorter survival and poorer prognosis. The prognosis of patients with highly differentiated, low to intermediate grade NET is relatively good, with a median survival of 223 months for those with early stage without metastasis, 111 months for those with regional invasion, and 33 months for those with distant metastasis.