Carcinoid tumors are part of a larger family of tumors called neuroendocrine tumors. Neuroendocrine tumors have the ability to secrete hormones and other substances into the bloodstream. Some neuroendocrine tumors start in endocrine organs like the thyroid gland. Carcinoid tumors do not start in a specific gland.
Carcinoid tumors are relatively rare.
They occur in only one or two individuals per 100,000. The cause of carcinoid tumors is not known. In most people, however, carcinoid tumors appear to occur by chance. Carcinoid tumors usually grow slowly, over the course of many years. It is not unusual for carcinoid tumors to be discovered by chance, during an endoscopy, X-ray, or surgery for something else.