What is carcinoid tumor? Carcinoid tumors are well-differentiated or moderately differentiated neuroendocrine tumors that occur in the stomach, small intestine, appendix, rectum, and lung. The most common type of carcinoid tumor is small bowel carcinoid tumor, which grows slowly but may develop lymph node metastasis and liver metastasis. Most patients with liver metastases have carcinoid syndrome. Carcinoid syndrome is not easy to recognize, and many patients are diagnosed with carcinoid tumor several years after the onset of symptoms. What is carcinoid syndrome? Certain hormones secreted by tumor cells of gastrointestinal carcinoid tumors enter into the bloodstream, and when the concentration reaches a certain amount, it can cause symptoms, such as diarrhea, flushing of the skin, and accelerated heart rate, etc., which is called carcinoid syndrome. Diagnosis can be helped by detecting Serotonin and its metabolite 5-HIAA in the blood. How is carcinoid tumor diagnosed? It can be diagnosed pathologically by surgical resection of the tumor, endoscopic biopsy, or puncture biopsy of the liver lesion, obtaining tissues that stain positively by immunohistochemistry for CgA and Syn. Patients with carcinoid tumors tend to have elevated levels of the laboratory tumor marker CgA, and its level is closely related to the size of the tumor. Urinary 5-HIAA and serum Serotonin are elevated in patients with carcinoid syndrome. Octreotide scans are useful in detecting the primary site of carcinoid tumor and metastatic lesions. Treatment of carcinoid tumor? Treatment aims include removal of the tumor and control of symptoms. The most common site of carcinoid tumors is the small intestine, followed by the appendix. Surgical removal of the tumor is the main treatment for carcinoid tumors. When carcinoid tumor develops liver metastasis, liver tumor resection or hepatic artery embolization are the treatment options. When carcinoid syndrome occurs, it is necessary to control the symptoms. Currently, drugs that can effectively control carcinoid syndrome include octreotide and lanreotide. New drugs for targeted therapy are also in clinical trials, bringing new hope to patients with carcinoid metastasis. How to monitor the efficacy of treatment and changes in disease? Regular monitoring of blood CgA, urine 5-HIAA and serum Serotonin can reflect the progress of the tumor in the body and can also be used to monitor the efficacy of treatment.