Gastrointestinal Stromal Tumor (GIST)

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What is Gastrointestinal Stromal Tumor (GIST)?

A tumor begins when normal cells change and grow uncontrollably. A tumor can be benign (noncancerous) or malignant (cancerous, meaning it can spread to other parts of the body).

A gastrointestinal stromal tumor (GIST) is a type of tumor that occurs in the gastrointestinal (GI or digestive) tract, including the esophagus, stomach, gallbladder, liver, small intestine, colon, rectum, and lining of the gut. A GIST is different than other, more common types of gastrointestinal tumors because of the type of tissue in which they start. Originally, GISTs were thought to be either muscle or nerve tumors, but recent research shows that GISTs start in cells found in the walls of the GI tract, called interstitial cells of Cajal (ICC). These cells send signals to the GI tract to help move food and liquid through the system.

GISTs belong to a group of cancers called soft tissue sarcoma. Soft tissue sarcomas are a group of cancers that develop in the tissues that support and connect the body, and the sarcoma cells resemble the cells that hold the body together, including fat cells, muscles, nerves, tendons, joints, blood vessels, or lymph vessels.

It is important to note that all GISTs can become cancerous. Sometimes it may be hard for the doctor to tell immediately whether a GIST is likely to come back after its surgical removal. As a result, the doctor will look at many factors to determine the best treatment, including the size of the tumor, whether it has already spread, how many dividing cells there are, and the tumor’s location.

Symptoms & Signs

People with GIST may experience many different symptoms or signs. Sometimes, people with GIST do not show any of these symptoms. Or, these symptoms may be caused by a medical condition that is not a tumor. If you are concerned about a symptom or sign on this list, please talk with your doctor. GISTs are not usually found at an early stage because they often do not cause specific symptoms. When symptoms do occur, they may be vague and can include:

Pain or discomfort in the abdomen

A mass in the abdomen that you can feel with your hand

Nausea and vomiting

Vomiting blood or having blood in the stool

Fatigue due to anemia (low red blood cell counts)

Your doctor will ask you questions about the symptoms you are experiencing to help find out the cause of the problem, called a diagnosis. This may include how long you’ve been experiencing the symptom(s) and how often.

If a tumor is diagnosed, relieving symptoms and side effects remains an important part of cancer care and treatment. This may also be called symptom management, palliative care, or supportive care. Be sure to talk with your health care team about symptoms you experience, including any new symptoms or a change in symptoms.

Risk Factors

A risk factor is anything that increases a person’s chance of developing a tumor. Although risk factors often influence the development of a tumor, most do not directly cause the disease. Some people with several risk factors never develop a tumor, while others with no known risk factors do. However, knowing your risk factors and talking about them with your doctor may help you make more informed lifestyle and health care choices.

The majority of GISTs develop for no known reason, called sporadic. Doctors are rarely able to find a specific risk factor for patients diagnosed with GIST, other than the hereditary syndromes discussed below.

Family history. GIST rarely runs in families, and having a family member with GIST does not always increase your risk of developing the disease. Hereditary syndromes that can increase the risk of GIST include neurofibromatosis Type 1 (NF1) and Carney-Stratakis Dyad.

Most often, GIST, including non-hereditary tumors, begins because of genetic mutations (changes). The two most common genes affected are called KIT and platelet-derived growth factor receptor(PDGFR). Increasingly, researchers are finding mutations in other genes, such as a protein called succinate dehydrogenase (SDH), or BRAF, a gene occasionally changed in patients with melanoma or colorectal cancer. Testing for these mutations may be available at hospitals that specialize in treating GIST. Researchers continue to look for specific genes and other syndromes that may be related to the development of GIST and which may be used to help choose a patient’s treatment options.

Because no non-hereditary, preventable risk factors have been found, there is no good way to prevent GIST.

Diagnosis

Doctors use many tests to diagnose a tumor and find out if it is cancerous and, if so, if it has metastasized (spread). Some tests may also determine which treatments may be the most effective. For most types of tumors, a biopsy is the only way to make a definitive diagnosis. If a biopsy is not possible, the doctor may suggest other tests that will help make a diagnosis. Imaging tests may be used to find out whether the cancer has metastasized. Your doctor may consider these factors when choosing a diagnostic test:

Age and medical condition

Type of tumor suspected

Severity of symptoms

Previous test results

In addition to a physical examination, the following tests may be used to diagnose GIST or determine the best treatment:

Computed tomography (CT or CAT) scan.  A CT scan creates a three-dimensional picture of the inside of the body with an x-ray machine. A computer then combines these images into a detailed, cross-sectional view that shows any abnormalities or tumors. Sometimes, a contrast medium (a special dye) is injected into a vein to provide better detail. For patients with GIST, the CT scan is the most commonly used way to diagnose the disease. A CT scan can help doctors determine whether the cancer has spread to the liver. 

Fecal occult blood test. This test detects occult (hidden) blood in the stool, which can be caused by cancer in the GI tract. A small amount of stool is placed on a plastic slide or special paper and is tested in the doctor's office or a laboratory.

X-ray. An x-ray is a way to create a picture of the structures inside of the body, using a small amount of radiation. X-rays may be taken of the esophagus and stomach, which are referred to as the upper GI tract. This procedure is also called a barium swallow, because the x-rays are taken after a patient drinks a substance called barium, which outlines the GI tract on the x-ray and helps the doctor see a tumor or other abnormal areas. In a barium enema, the doctor looks at the lining of the colon and rectum on the x-ray after the barium is given through the anus.

Endoscopy. This test allows the doctor to see the inside of the stomach. The patient may be sedated, and the doctor inserts a thin, lighted tube called a gastroscope through the mouth, down the esophagus, and into the stomach and small bowel. If abnormal areas are found, the doctor can remove a sample of tissue and check it for evidence of cancer (see Biopsy, below).

Endoscopic ultrasound. This test is similar to an endoscopy, but the gastroscope has a small ultrasound probe on the end that uses sound waves to create an image of the stomach and nearby organs. The ultrasound image helps doctors determine if or how far the cancer has spread into the stomach and nearby tissues.

Magnetic resonance imaging (MRI). An MRI uses magnetic fields, not x-rays, to produce detailed images of the body. A contrast medium may be injected into a patient’s vein to create a clearer picture.

Positron emission tomography (PET) scan. A PET scan is a way to create pictures of organs and tissues inside the body. A small amount of a radioactive substance is injected into a patient’s body. This substance is absorbed mainly by organs and tissues that use the most energy. Because cancer tends to use energy actively, it absorbs more of the radioactive substance. A scanner then detects this substance to produce images of the inside of the body. PET scans are often used to add to the information from the CT scan, MRI, and physical examination, and may be used to show early growth of the disease (called PET flare), or to measure how well treatment is working.

Biopsy. It is very important that a patient is seen by a team of medical and surgical oncologists experienced in the treatment of GIST before a big surgery is performed. A biopsy may be recommended if a mass suspected of being GIST is found. A biopsy is the removal of a small amount of tissue for examination under a microscope. Other tests can suggest that cancer is present, but only a biopsy can make a diagnosis. The sample removed from the biopsy is analyzed by a pathologist (a doctor who specializes in interpreting laboratory tests and evaluating cells, tissues, and organs to diagnose disease). The type of biopsy performed will depend on the location of the tumor. Sometimes, surgery is recommended even if the biopsy results do not indicate cancer, as a biopsy for GIST is not always definitive. In some instances, an entire tissue mass or an organ will be removed to make a diagnosis.

Molecular testing of the tumor. Your doctor may recommend running laboratory tests on a tumor sample to identify specific genes, proteins, and other factors unique to the tumor. Recent studies have shown that depending on the tumor’s specific gene mutations, some patients may need higher doses of a medicine called imatinib (Gleevec) to best control the tumor. Currently this testing is being offered within and outside of clinical trials (research studies). Also, because knowing the exact type of gene mutation in GIST helps determine how well treatment with imatinib will work, testing each patient for genetic mutations can help doctors target the specific mutation causing the tumor to grow.

After these diagnostic tests are done, your doctor will review all of the results with you. If the diagnosis is GIST, these results also help the doctor describe the tumor; this is called staging. 

Stages

Staging is a way of describing where the tumor is located, if or where it has spread, and whether it is affecting the functions of other organs in the body. Doctors use diagnostic tests to determine the tumor's stage, so staging may not be complete until all the tests are finished. Knowing the stage helps the doctor to decide what kind of treatment is best and can help predict a patient's prognosis (chance of recovery). There are different stage descriptions for different types of cancers.

One tool that doctors use to describe the stage of other types of cancer is the TNM system. This system judges three factors: the tumor itself (T), the lymph nodes (N) around the tumor, and if the tumor has spread to other parts of the body (metastasis, M). The results are combined to determine the stage of cancer for each person.

However, the use of the TNM system for GIST is not considered standard practice. Instead, doctors look at different factors to help determine a patient’s prognosis and the specific risk of how aggressive an individual tumor will be. Specifically, they want to determine how quickly it may grow and the likelihood of the tumor recurring (coming back) after surgery. Doctors use the factors listed below to determine how aggressive a tumor will be:

The size of the tumor

The mitotic count (the actual number of dividing cells)

The location where the tumor started.

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