Gastrointestinal stromal tumors (GISTs) are tumors that arise from a specific type of cell that is part of the autonomic nervous system in the gastrointestinal (GI) tract. The GI system is an important group of organs. It includes the esophagus, stomach, and both small and large intestines. The GI system is responsible for moving food through the body, digesting and absorbing nutrients from food, and producing waste.

When a GIST forms, it can stay unnoticed for some amount of time, depending on where it is in the GI system and how fast it’s growing. Symptoms of GISTs show up as the tumor becomes large enough to cause malfunction of the GI system or other parts of the body. Some GISTs are small and are found by chance during an imaging test or other procedures.

How do GISTs form?

Tumors form when cells in the body begin to grow out of control. GISTs develop from a certain type of cell in the GI system when the cells are very young. These cells are called the interstitial cells of Cajal (ICCs).

ICCs belong to the part of the nervous system responsible for controlling body processes, such as digesting food. The cells signal the muscles along the GI tract to contract and relax. This motion moves food through the GI system.

About 50 to 60 percent of GISTs start in the stomach, while about 20 to 30 percent start in the small intestine. They can form anywhere along the GI tract, from the esophagus to the rectum. In rare cases, they can form in tissue layers that encase the GI tract. GISTs can be cancerous, but not always. Doctors can determine if a GIST is cancerous by performing a biopsy and having the cells evaluated under a microscope.

What causes a GIST?

The direct cause of GISTs remains unknown. However, in recent years scientists have begun to learn more about what causes normal cells to become cancerous. They have found that our DNA plays a large part in the development of cancer.

Our DNA is responsible for our physical traits, which we inherit from our parents. But DNA also provides our bodies with the blueprints it needs to grow, develop, and function. Certain genes within our DNA are responsible for controlling how cells grow and divide.

Genes called oncogenes tell cells to grow and divide, while tumor suppressor genes slow down or stop cell growth. A random mutation in a cell can turn on an oncogene or turn off a tumor suppressor gene. This causes the cell to grow and divide at an abnormal pace. This is how cancer starts.

What are the symptoms of a GIST?

As GISTs grow, they can push into nerves, blood vessels, or other organs. This can lead to the bleeding associated with GISTs. The most common symptom of a GIST is GI bleeding. This bleeding can be acute and show up in vomit or stool. Or the bleeding can be very subtle and cause a low red blood cell count. This condition is called anemia.

GIST can also lead to general, nonspecific symptoms such as:

  • weakness
  • fatigue
  • weight loss
  • nausea
  • vomiting
  • fever

When large enough, GISTs can also cause:

  • feelings of fullness after eating a small amount
  • difficulty swallowing, known as dysphagia
  • abdominal pain and discomfort

Sometimes, a GIST can lead to a blockage in the intestine called a bowel obstruction. The specific symptoms depend on the location of the tumor along the GI tract.