What Is a GIST? Understanding Gastrointestinal Stromal Tumors

What Is a Gastrointestinal Stromal Tumor (GIST)?

A gastrointestinal stromal tumor, or GIST, is a type of tumor that grows in the wall of the digestive tract. GISTs belong to a family of cancers called soft tissue sarcomas, which means they develop from the body’s connective and supporting tissues rather than from the surface lining where more common cancers like colon or stomach cancer begin. Because GISTs are relatively rare, many people have never heard of them until they or a loved one receive a diagnosis.

If you have recently been diagnosed, it is natural to feel overwhelmed. The good news is that GIST is one of the most treatable sarcomas, and understanding the basics can help you feel more prepared for conversations with your care team.

Where Do GISTs Form in the Body?

GISTs can arise anywhere along the gastrointestinal (GI) tract, which runs from the esophagus to the rectum. However, they show up far more often in some locations than others:

• Stomach — the most common site, accounting for roughly 60 percent of cases.
• Small intestine — the second most common location, about 30 percent of cases.
• Esophagus, colon, and rectum — less common sites.
• Outside the GI tract — in rare instances a GIST may develop in nearby tissues such as the omentum or mesentery.

Tumors can range from very small nodules found incidentally during an unrelated procedure to larger masses that produce noticeable symptoms.

What Causes a GIST? The Role of Interstitial Cells of Cajal

GISTs are thought to develop from, or share features with, specialized cells called the interstitial cells of Cajal. These cells act as the natural pacemakers of the digestive tract, sending the electrical signals that coordinate the muscle contractions that move food along. When these cells, or their precursors, grow in an uncontrolled way, a GIST can form.

In most cases, this uncontrolled growth is driven by a change, or mutation, in one of two genes:

• KIT — mutations in this gene are found in the majority of GISTs. The KIT gene makes a protein that acts like an on-off switch for cell growth. A mutation can leave that switch stuck in the on position.
• PDGFRA — a smaller share of GISTs are driven by mutations in this related gene, which behaves in a similar way.

A smaller group of GISTs have neither of these mutations and are sometimes called wild-type GISTs. Identifying which mutation is present matters, because it can influence how the tumor is expected to behave and how well certain medications may work. This is one reason molecular testing of the tumor is so valuable.

What Symptoms Can a GIST Cause?

Many small GISTs cause no symptoms at all and are discovered by chance during imaging or an endoscopy performed for another reason. When symptoms do occur, they are often related to the tumor’s size and location. Common signs include:

• Vague abdominal discomfort or a feeling of fullness
• A mass that can sometimes be felt in the abdomen
• Nausea, vomiting, or loss of appetite
• Fatigue, which may be linked to slow blood loss and anemia
• Blood in the stool or vomit, or dark, tarry stools

Because these symptoms overlap with many far more common and less serious digestive conditions, they are not proof of a GIST. Still, persistent or unexplained symptoms always deserve evaluation by a physician.

How Common Are GISTs?

GISTs are uncommon. Estimates suggest that only a few thousand new cases are diagnosed in the United States each year, which places GIST firmly in the category of rare tumors. They can occur at any age but are most often diagnosed in adults over 50, and they affect men and women at similar rates. A small number of GISTs are linked to inherited genetic syndromes, though the great majority arise sporadically with no family history.

Because GISTs are rare, general oncologists and surgeons may see only a handful over an entire career. Care at a center with specific experience in GIST can make a meaningful difference in accurate diagnosis and thoughtful treatment planning.

Moving Forward After a GIST Diagnosis

Learning that you have a GIST can be frightening, but knowledge is a powerful first step. GISTs are generally well understood, and there are effective treatment options, including surgery and targeted medications, tailored to the individual tumor. Every GIST is different, and the right plan depends on the tumor’s size, location, mutation profile, and your overall health. The most important next step is to partner with a physician who has deep experience treating this specific disease, so your care can be personalized to your situation.

Frequently Asked Questions