Carcinoid syndrome refers to the fact that carcinoid tumors can occur in any part of the GI tract except the esophagus, with those located in the appendix accounting for 1/3 of cases, mostly in women, and rarely metastasizing. The rest are located in the duodenum, colon (mostly in men), gallbladder and Merkel’s diverticulum, etc. It can also occur in the bronchi and ovaries, but it is less common. If it occurs in the small intestine, the malignancy is large and can metastasize to the lungs, bones and other intra-abdominal organs. Prevention: 1.Regular examination, timely detection and surgery. 2.Follow up well after treatment. 3.As the cause of this disease has not been fully elucidated, mainly pay attention to some risk factors of diet and environment that cause tumor.