Gastrointestinal Stromal Tumors (GIST)

What is GIST?

Gastrointestinal stromal tumors, or GISTs, are a relatively uncommon type of cancer that occurs in the gastrointestinal (GI) tract (the esophagus, stomach, small intestine and colon). GISTs belong to a class of diseases called sarcomas, cancers that begin in the connective tissues, which include fat, muscle, blood vessels, deep skin tissues, nerves, bones and cartilage.

GISTs originate in cells called stroma, which are located along the GI tract and are part of the system that signals the body to help move food through the digestive system. Approximately 50% of GISTs occur in the stomach, 25% in the small intestine, 10% in the colon and 15% other parts of the GI tract.

 

How many people develop GIST?

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. Most cases occur in people between 40 and 80 years of age, although GIST may also occur in much younger individuals.

 

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 (CDl17), 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.

Recently, an expert panel concluded that all GISTs, regardless of their size or location, may be malignant (have the ability to spread). Even after a GIST is removed, it may come back in the same area or may metastasize (spread) outside of the GI tract.

 

Why GIST Develops (Pathophysiology)

The way in which GIST grows or the route the tumor takes when it spreads through the body is called its pathophysiology.

Scientists are beginning to unravel some of the processes that go on inside cells that cause them to develop into GISTs. Normally these cells, like other cells in the body, grow and divide in a controlled fashion. But sometimes things can go wrong, allowing these cells to grow out of control and ultimately become cancerous.

Scientists have discovered that connective tissue cells may grow in an uncontrolled manner as the result of an abnormality in their genetic makeup or DNA. For most GISTs, a specific change or mutation in the DNA causes a cellular enzyme, known as Kit to be switched "on" all the time. Kit is an enzyme (called a "tyrosine kinase") responsible for sending growth and survival signals inside the cell. If it is ON, the cell stays alive and grows or proliferates. The overactive, uncontrolled mutant Kit enzyme triggers the uncontrolled growth of GIST tumor cells. This insight into the way GISTs develop has helped to identify new treatment options for this sarcoma.

 

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