Gastrointestinal Stromal Tumors, or GISTs, are a relatively uncommon type of cancer that occurs in the gastrointestinal (GI) tract. GISTs are believed to 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 gastrointestinal 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.

Although these tumors can start anywhere in the GI tract, they occur most often in the stomach (50% to 70%) or the small intestine (20% to 30%). The rest are found in the esophagus, large intestine (colon and rectum), and anus.

How many people develop Gastrointestinal Stromal Tumors?

Until recently, GISTs were thought to be extremely rare. However, recent advances in diagnosis and classification methods have shown that GISTs may be more common than previously believed. Based on data from a Swedish epidemiology study, experts believe that in the U.S., as many as 4,500 to 6,000 new cases of GIST occur each year. Of these, about 1,500 have already spread to distant sites when they are initially found.

Risk Factors

There are no known factors that have specifically been identified as increasing a patient's risk for GIST. The disease is thought to be predominantly caused by a mutation or change in an enzyme called Kit (CD117), which is found on the surface of normal cells. In healthy individuals, the role of Kit is to signal cells to grow and divide. However, in patients with GIST, a malfunctioning Kit signals the cells to constantly grow and divide out of control, and they become cancerous.

In rare cases, GISTs have been found in several members within the same family. These family members inherited a gene mutation, usually the c-Kit that leads to GIST. But most GISTs are sporadic (they are not passed down from generation to generation), and their cause is unknown.

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