The gastrointestinal system

The gastrointestinal (GI) system processes food for energy and rids the body of solid waste. It is also known as the digestive system. 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 breathing muscle under 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. It is the longest section of the gastrointestinal (GI) tract, measuring more than 20 feet.

The small intestine joins the large intestine (colon), a muscular tube about 5 feet long. The colon absorbs water and mineral nutrients from the food matter and serves as a storage place for waste. The waste left after this process goes into the rectum as stool (feces). From there it passes out of the body through the anus.

Gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) are fairly rare tumors of the GI tract. In the past, they were thought to start in muscle or nerve cells in the GI tract. This is because the tumor cells look like muscle or nerve cells under the microscope.

We now know that GISTs start in special cells found in the wall of the GI tract, called the interstitial cells of Cajal (ICCs), or in very early cells that can develop into ICCs. ICCs are part of the autonomic nervous system, the part of the nervous system that regulates body processes. The autonomic nervous system sends signals to the GI tract telling it to digest food. ICCs are sometimes called the "pacemakers" of the GI tract because they send signals to the muscles in the digestive system, telling them to contract to move food and liquid through the GI tract.

Not all GISTs are cancerous. Some are benign -- they don't grow into other areas or spread to other parts of the body. Ways to try to determine whether a GIST is benign or cancerous are discussed further in the section "How are gastrointestinal stromal tumors diagnosed?"

Other gastointestinal 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.

Some parts of the GI tract, such as 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 that are 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. Neuroendocrine cancers can develop from these cells. This type of cancer is rare in the GI tract. Carcinoid tumors are an example of a neuroendocrine cancer found in the GI tract.

Other rare types of cancer that can be seen in the GI tract include leiomyosarcoma, angiosarcoma, and peripheral nerve sheath tumors. These arise from muscle cells, blood vessel cells, and nerve cells in the GI tract.

GISTs are different from these other GI tract cancers. First of all, they start in different types of cells. GISTs are also quite different in their prognosis (outlook) and their treatment. For these reasons, doctors need to figure out whether a patient has a GIST, some other type of cancer, or a non-cancerous condition.

It is also important for patients to understand that GISTs are not the same as other, more common types of GI tract cancers. By learning more about GISTs, patients can better take part in their health care and make informed decisions about treatment options.

Last Medical Review: 05/11/2009
Last Revised: 05/11/2009