What are gastrointestinal stromal tumors?
To understand gastrointestinal stromal tumors, it helps to know something about the structure and function of the gastrointestinal system, also known as the digestive system.
The gastrointestinal system
The gastrointestinal (GI) system (or digestive system) processes food for energy and rids the body of solid waste. After food is chewed and swallowed, it enters the esophagus, a tube that carries food through the neck and chest to the stomach. The esophagus joins the stomach just beneath the diaphragm (the thin band of muscle below the lungs).
The stomach is a sac-like organ that holds food and helps the digestive process by secreting gastric juice. The food and gastric juices are mixed into a thick fluid called chyme that is then emptied into the small intestine. The small intestine continues breaking down the food and absorbs most of the nutrients into the bloodstream. This is the longest section of the GI tract, measuring more than 20 feet.
The small intestine joins the large intestine, the first part of which is the colon, a muscular tube about 5 feet long. The colon absorbs water and mineral nutrients from the remaining food matter. The waste left after this process goes into the rectum as stool (feces), where it is stored until it passes out of the body through the anus.
Gastrointestinal stromal tumors
Gastrointestinal stromal tumors (GISTs) are uncommon tumors of the GI tract. These tumors start in very early forms of special cells found in the wall of the GI tract, called the interstitial cells of Cajal (ICCs). ICCs are cells of the autonomic nervous system, the part of the nervous system that regulates body processes such as digesting food. ICCs are sometimes called the “pacemakers” of the GI tract because they signal the muscles in the digestive system to contract to move food and liquid through the GI tract.
More than half of GISTs start in the stomach. Most of the others start in the small intestine, but GISTs can start anywhere along the GI tract. A small number of GISTs start outside the GI tract in nearby areas such as the omentum (an apron-like layer of fatty tissue that hangs over the organs in the abdomen) or the peritoneum (the layer of tissue that lines the organs and walls of the abdomen).
Not all GISTs are cancerous. Some are benign (not cancerous) and don’t grow into other areas or spread to other parts of the body. Doctors have ways to find out whether a GIST is benign or cancerous. These are discussed in the section, “How are gastrointestinal stromal tumors diagnosed?”
Other gastrointestinal tract cancers
It is important to understand that GISTs are not the same as other, more common types of GI tract cancers.
Cancers can occur anywhere in the GI tract − from the esophagus to the anus. Usually, these cancers start in glandular cells that line most of the GI tract. The cancers that develop in these cells are called adenocarcinomas. Most cancers of the GI tract, including those of the esophagus, stomach, colon, and rectum, are adenocarcinomas.
Some parts of the GI tract, like the upper part of the esophagus and the end of the anus, are lined with flat cells called squamous cells. These are the same type of cells found on the surface of the skin. Cancers starting in these cells are called squamous cell carcinomas.
The GI tract also has neuroendocrine cells. These cells have some features in common with nerve cells but other features in common with hormone-producing (endocrine) cells. Cancers that develop from these cells are called neuroendocrine tumors. These cancers are rare in the GI tract. Carcinoid tumors are an example of a neuroendocrine tumor found in the GI tract.
Other rare types of cancer in the GI tract include leiomyosarcomas (cancers of smooth muscle cells), angiosarcomas (cancers of blood vessel cells), and peripheral nerve sheath tumors (cancers of cells that support and protect nerves).
GISTs are different from these other GI tract cancers. They start in different types of cells, need different types of treatment, and have a different prognosis (outlook). This is why doctors need to figure out whether a person with a tumor in the GI tract has a GIST, some other type of cancer, or a non-cancerous condition.
Last Medical Review: 04/04/2014
Last Revised: 05/09/2014