Neuroendocrine Tumor of the Gastrointestinal Tract: Introduction

Approved by the Cancer.Net Editorial Board, 08/2018

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 Neuroendocrine Tumor of the Gastrointestinal Tract. Use the menu to see other pages. Think of that menu as a roadmap for this complete guide.

About neuroendocrine tumors

A tumor begins when the DNA of healthy cells is damaged, causing the cells to change and grow out of control, forming a mass. A tumor can be cancerous or benign. A cancerous tumor is malignant, meaning it can grow and spread to other parts of the body if it is not found early and treated. A benign tumor means the tumor can grow but will not spread. A benign tumor usually can be removed without it causing much harm.

A neuroendocrine tumor (NET) begins in the specialized cells of the body’s neuroendocrine system. These cells have traits of both hormone-producing endocrine cells and nerve cells. They are found throughout the body’s organs and help control many of the body’s functions. All NETs are considered malignant tumors.

NETs develop most commonly in the gastrointestinal (GI) tract or in the lungs (learn more about NETs of the lung). GI tract NETs and lung NETs used to be called carcinoid tumors. NETs can also develop in the pancreas (learn more about NETs of the pancreas) and other locations throughout the body. A rare type of NET that develops in the adrenal gland is called pheochromocytoma. Learn more about NETs that develop in other parts of the body.

About GI tract NETs

NETs can develop in any part of the body. The most common places they form is the GI tract or digestive system, specifically the small intestine and appendix. The GI tract, which starts at the esophagus and ends at the anus, plays a central role in digesting food and liquid and in processing waste. Neuroendocrine cells perform specific functions in the GI tract, such as controlling how quickly food moves through it.

Here is a general overview of where GI tract NETs begin:

  • 39% occur in the small intestine.

  • 15% occur in the rectum.

  • 7% occur in the appendix.

  • 5% to 7% occur in the colon.

  • 2% to 4% occur in the stomach.

Because these tumors develop from neuroendocrine cells, they can make high levels of hormone-like substances called neuropeptides and amines. About 40% of NETs release hormones that lead to symptoms. These tumors are called “functional.” Carcinoid syndrome (see Symptoms and Signs) is a classic type of functional NET and is associated with the release of a substance called serotonin (see Diagnosis). In other tumors, the hormone-like substances may not be released in large enough amounts to cause symptoms, or the substances may be defective and not cause symptoms. These NETs are called “non-functional.”

The next section in this guide is Statistics. It helps explain the number of people who are diagnosed with a GI tract NET and general survival rates. Use the menu to choose a different section to read in this guide.