Gastrointestinal Stromal Tumors

What Are Gastrointestinal Stromal Tumors?

The Gastrointestinal (Digestive) System

The 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 breathing muscle under the lungs).

The stomach is a sac-like organ that holds food and begins 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 over 20 feet.

The small intestine joins the colon, a muscular tube of 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. 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, some were thought to start in the muscle layer of the GI tract, and some were thought to start in nerve cells. This is because the tumor cells look like muscle or nerve cells under the microscope. They were often thought to be related to sarcomas -- cancers that start in the muscle, bones of the legs and arms, or other connective tissues.

We now know that these tumors are in fact not true muscle or nerve tumors. Most doctors believe they 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, which sends signals to the GI tract. Some have called these cells the "pacemakers" of the GI tract. The nerve signals they send cause muscles of the digestive organs to contract, which helps to move food and liquid through the GI tract.

Not all GISTs are cancerous. Some are benign -- they don't invade 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?"

Difference Between GISTs and Other GI Tract Tumors

Cancers can occur anywhere in the GI tract from the esophagus to the anus.

Most cancers in the GI tract start in glandular cells lining the GI tract. These cells can develop into adenomas (non-cancerous tumors of gland cells) or adenocarcinomas (cancers of gland cells).

In some parts of the GI tract, mostly in the upper part of the esophagus and at the end of the anus, there are 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.

Neuroendocrine cancers such as carcinoid tumors are a relatively uncommon type of cancer that can also occur in the gastrointestinal tract. They develop from neuroendocrine cells, which have some features of nerve cells and in other ways resemble hormone producing (endocrine) cells.

GISTs are different from these more common GI tract cancers, in large part because they start in different types of cells. GISTs are also quite different in their prognosis (outlook for survival) and their treatment. For these reasons, doctors need to figure out whether a patient has a GIST, an adenoma, an adenocarcinoma, a neuroendocrine cancer, some other type of tumor, or a non-cancerous condition.

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

Do We Know What Causes Gastrointestinal Stromal Tumors?

In recent years, scientists have made great progress in learning how certain changes in DNA can cause normal cells to become cancerous. DNA is the chemical that carries the instructions for nearly everything our cells do. We look like our parents because they are the source of our DNA. But DNA affects more than our outward appearance. Some genes (parts of our DNA) contain instructions for controlling when cells grow and divide.

Every time a cell prepares to divide into 2 new cells, it must duplicate its DNA. This process is not perfect and, sometimes, copying errors (mutations) occur, especially if the cells are growing rapidly.

Certain genes that promote cell growth and division are called oncogenes. Others that slow down cell division or cause cells to die at the right time are called tumor suppressor genes. We know that cancers can be caused by DNA mutations (defects) that turn on oncogenes or turn off tumor suppressor genes.

Some people with certain types of cancer have DNA mutations they inherited from a parent, which increased their risk for the disease. There are a few families that have GISTs caused by inherited mutations. But most DNA mutations related to GISTs are not inherited. These mutations occur for no apparent reason.

We do not know the exact cause of GIST. However, we do know that there is a change in an oncogene called c-kit of almost all patients with GIST. The c-kit gene is found in all cells of the body. It leads to the formation of a protein called KIT. This protein causes the cell to grow and divide. Usually the c-kit gene is inactive. It is only activated if there is a need for more interstitial cells of Cajal (ICCs). In most GISTs the c-kit gene is mutated and is always active. This may explain why the cancer forms. The cells are always growing and dividing. In families that have many members with GISTs, doctors have found inherited mutations of the c-kit gene.

In some GISTs, a different gene mutation causes the cell to make too much of a protein called PDGFRA. This has the same effect on the cell as does KIT.

These proteins (KIT and PDGFRA) act as enzymes called tyrosine kinases. These are important in the diagnosis and treatment of GIST.

Can Gastrointestinal Stromal Tumors (GIST) Be Found Early?

Screening refers to tests and exams used to find a disease such as cancer in people who do not have any symptoms. The American Cancer Society has recommendations for screening tests to find several types of cancer as early as possible. But because GISTs occur so rarely, no effective screening tests have been found, so routine testing of people without any symptoms is not recommended.

GISTs may be found early by chance. Sometimes they are seen on an exam for another problem, such as during colonoscopy to look for colon cancer. Or a GIST may be seen on an imaging test, such as a CT scan or barium study, performed for another reason, but this is very uncommon.

GISTs may also be found incidentally (unexpectedly) during abdominal surgery for another problem.

How Are Gastrointestional Stromal Tumors Treated?

This information represents the views of the doctors and nurses serving on the American Cancer Society's Cancer Information Database Editorial Board. These views are based on their interpretation of studies published in medical journals, as well as their own professional experience.

The treatment information in this document is not official policy of the Society and is not intended as medical advice to replace the expertise and judgment of your cancer care team. It is intended to help you and your family make informed decisions, together with your doctor.

Your doctor may have reasons for suggesting a treatment plan different from these general treatment options. Don't hesitate to ask him or her questions about your treatment options.