What is GIST?

GIST is an abbreviation for gastrointestinal stromal tumor, a rare cancer of the gastrointestinal tract.

What is a gastrointestinal stromal tumor?

Gastrointestinal stromal tumor (abbreviated and often referred to as GIST) is a rare cancer of the gastrointestinal (GI) tract. Most GISTs develop in the stomach or in the small intestine, and a small percentage develops elsewhere in the GI tract. GIST is difficult to diagnose and to treat because it "hides" in the abdomen and often does not cause any symptoms.

When GIST first develops, the tumor stays in one area, such as the stomach. This is referred to as the primary or original tumor site. GISTs that stay in their original location are called localized tumors. However, when GISTs advance, they can spread to other parts of the body. When a GIST spreads, it becomes a metastatic tumor, or a tumor that has metastasized. GISTs often grow quite large before they are discovered, and they often spread to other organs, such as the liver.

Scientists have discovered the defect, or mutations, that cause GISTs to grow. Now there are treatments that can block tumor growth signals.

What causes GIST?

GIST has no known causes related to environmental factors or behavioral habits. GIST results from gene mutations (defects) that are thought to be random in most cases.

Almost all GISTs start when a gene, called kit, develops a mutation and forms a protein called KIT. GISTs are caused by cells that grow and divide faster than they should. Most of the time, this excessive growth is caused by the abnormal KIT protein. (A protein is an essential component of all living cells that is made up of smaller components called amino acids.) GISTs tend to build up an excess amount of the KIT protein, which causes them to test "positive" for KIT. Approximately, 95% of GISTs are KIT-positive (abbreviated as KIT+).

KIT protein sends a signal that tells cells when to grow and divide. Usually, this signal is only "on" when more cells are needed. A KIT+ GIST occurs when the signal is continuously activated. When this happens, the abnormal KIT protein tells certain cells to grow and divide even when they are not needed. Unlike in normal cells, this abnormal KIT protein never turns "off." This causes the cells to multiply out of control, forming a tumor.

These abnormal cells keep growing and dividing, eventually becoming cancerous. Cancerous GIST cells develop a survival "advantage" because they grow faster and live longer than the healthy surrounding cells. The longer the cancerous cells live, the more likely it is that they will become dangerous and spread (metastasize) to the other parts of the body. That is why it is so important to control these cells by treating KIT+ GIST.

How common is GIST?

GISTs are not common, and the exact number of people diagnosed with this tumor type each year is not known. There are an estimated 3300 to 6000 new cases reported each year in the United States. At diagnosis, approximately 2500 of these cases are metastatic —cancer that has spread from its primary site in the body to another site.

Although GISTs occur predominantly in adults, they can occur at any age. The average age at diagnosis is between 40 and 60 years. The incidence of GISTs is slightly higher in men than in women.

Where in the body do GISTs most often occur?

The majority of GISTs arise in the stomach (50% to 70%) or small intestine (20% to 30%). However, they can occur anywhere along the gastrointestinal (GI) tract—esophagus, rectum, colon, and, rarely, in other locations. GISTs have a high risk of growth and may spread (metastasize) from the primary (original) tumor site to other locations in the body if not treated. In GIST the most common sites for metastasis are the liver and the abdominal membranes. GISTs can also spread to the lungs, lymph nodes, and other locations outside of the abdomen, but these are very uncommon.

How is GIST diagnosed?

Many patients with KIT+ GIST experience no symptoms in the early stages. They are "asymptomatic." Therefore, diagnosis may follow the identification of lesions as a result of unrelated exams or surgeries. Because many GISTs produce few symptoms, the cancer has often spread before being discovered. As the tumors grow larger, symptoms may increase in intensity and may include :

If GIST is suspected, a technique called staining can be used for confirmation. KIT staining confirms the presence of the KIT protein. KIT is the most common tumor marker for GIST, with 95% of GISTs staining positive for KIT. Staining is the most reliable way to make an accurate diagnosis and begin the necessary and appropriate GIST treatment.

Are all GISTs cancerous?

All GISTs have the potential to be cancerous (malignant). For this reason, the older terms malignant and benign are no longer used to describe these tumors. While some gastrointestinal stromal tumors might be low risk for cancer, other GISTs can be cancerous. Cancerous GISTs have a high risk of growth and may spread in the body if not treated.

The clinical behavior of GISTs is unpredictable, and an assessment of the potential for malignancy is usually based primarily on the size and the proliferation characteristics of the tumor.

What type of tumor are gastrointestinal stromal tumors?

GISTs are soft-tissue sarcomas. Most other cancers are carcinomas, not sarcomas.

What is a sarcoma?

Sarcomas are cancers that grow from cells of the body's connective or supportive tissues such as bone, cartilage, tendons, nerves, fat, muscle, tissue around joints, or blood vessels. GISTs are considered soft-tissue sarcomas.

What are the risk factors for gastrointestinal stromal tumors?

A risk factor is anything that affects a person's chance of getting a disease such as cancer.

Currently, there are very few known risk factors for GIST. GIST does not appear to be caused by environmental factors (like toxins) or behavioral habits (like smoking). GIST results from gene mutations that are thought to be random in the vast majority of cases.

In rare cases, GISTs have been found in several members of the same family. These family members inherited a gene mutation that leads to GIST. But most GISTs are not passed down from generation to generation.