Carcinoid Tumor: Overview

Approved by the Cancer.Net Editorial Board, 03/2014

ON THIS PAGE: You will find some basic information about this disease and the parts of the body it may affect. This is the first page of Cancer.Net’s Guide to Carcinoid Tumors. To see other pages, use the menu on the side of your screen. Think of that menu as a roadmap to this full guide.

About the endocrine system and endocrine tumors

The endocrine system consists of cells that produce hormones. Hormones are chemical substances that are carried through the bloodstream to have a specific regulatory effect on the activity of other organs or cells in the body. Part of the endocrine system is the neuroendocrine system, which is made up of cells that are a cross between traditional hormone-producing cells and nerve cells.

A tumor begins when normal cells change and grow uncontrollably, forming a mass called a tumor. A tumor can be cancerous or benign. A cancerous tumor is malignant, meaning it can spread to other parts of the body. A benign tumor means the tumor will not spread and usually can be removed without it causing much harm.

An endocrine tumor is a mass that affects the parts of the body that produce and release hormones. Because an endocrine tumor develops from cells that produce hormones, the tumor itself can produce hormones and cause serious illness.

About carcinoid tumors

A carcinoid tumor starts in the hormone-producing cells of various organs. Carcinoid tumors most often develop in the gastrointestinal tract, in organs such as the stomach or intestines, or in the lungs. However, a carcinoid tumor can also develop in the pancreas, a man’s testicles, or a woman’s ovaries. More than one carcinoid tumor can occur in the same organ.

Here is a general overview of where carcinoid tumors begin:

  • 39% occur in the small intestine.
  • 15% occur in the rectum.
  • 10% occur in the bronchial system of the lungs.
  • 7% occur in the appendix.
  • 5% to 7% occur in the colon.
  • 2% to 4% occur in the stomach.
  • 2% to 3% occur in the pancreas.
  • About 1% occurs in the liver.
  • They rarely occur in ovaries, testicles, and other organs.

Because carcinoid tumors are a type of neuroendocrine tumor, they can make high levels of neuropeptides and amines (hormone-like substances). However, these substances may not be released in large enough amounts to cause symptoms, or the substances may be defective and not cause symptoms. As a result, a carcinoid tumor can grow slowly for many years without causing symptoms. Although a carcinoid tumor is cancerous, it is often described as "cancer in slow motion."

There are two subtypes of lung carcinoid tumors: typical and atypical. The difference is based on how a tumor processes and makes serotonin (5-HT). Serotonin is a neurotransmitter involved in behavior and depression.

  • A typical lung carcinoid tumor produces high levels of serotonin and chromogranin-A in the blood and high levels of 5-HIAA (a product of serotonin breakdown) in the urine.
  • An atypical lung carcinoid tumor produces normal levels of serotonin and chromogranin-A in the blood and normal levels of 5-HIAA in the urine but high levels of serotonin and 5-HTP (an amino acid) in the urine, and it can make 5-HTP.

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