Gastrointestinal stromal tumors (GISTs) are often found because of signs or symptoms a person is having. Others are found during exams or tests done for other problems. If cancer is suspected, further tests will be needed to confirm the diagnosis.
Signs and symptoms of gastrointestinal stromal tumors
Most GISTs occur in the stomach or small intestine. These tumors may not cause any symptoms unless they are in a certain location or grow to a certain size. Small tumors may not cause any symptoms and may be found accidentally when the doctor is looking for some other problem. These are often benign.
GISTs are often found because they cause bleeding into the intestinal tract. If the bleeding is fast enough, it can make bowel movements black and tarry. If the tumor bleeds into the stomach or esophagus, it may cause a person to vomit blood. Slower bleeding may not cause these problems, but over time it can lead to anemia (low red blood cell counts). This can cause a person to feel tired and weak.
Other possible symptoms of GISTs are:
- Abdominal (belly) discomfort or pain
- A mass or swelling in the abdomen
- Nausea, vomiting
- Feeling full after eating a small amount of food
- Loss of appetite
- Weight loss
- Problems swallowing (for tumors in the esophagus)
In some people the tumor may grow large enough to block the passage of food through the stomach or intestine. This is called an obstruction, and it causes severe abdominal pain and vomiting. Emergency surgery is often needed to treat the blockage.
If there is a reason to suspect that you may have a GIST, the doctor will use one or more methods to find out if it is cancer or something else. If it is cancer, further tests will be done to help determine the extent (stage) of the disease.
Medical history and physical exam
To learn your medical history, the doctor will ask you questions about your symptoms and any risk factors you may have. The doctor may ask about symptoms that might be caused by a mass in the esophagus, stomach, intestine, or rectum. A thorough physical exam can give your doctor more information about the possible signs of a GIST, like a mass in the abdomen, or other health problems.
Imaging tests
Imaging tests use x-rays, magnetic fields, or radioactive substances to create pictures of the inside of the body. Imaging tests may be done for a number of reasons, including:
- To help find out if a suspicious area might be cancer
- To learn how far cancer may have spread
- To help determine if treatment has been effective
- To look for signs that the cancer may have come back
Most patients who have or may have cancer will have one or more of these tests.
Barium x-rays
For these tests, a solution containing barium is used to coat the lining of the esophagus, stomach, and intestines. This makes abnormalities of the lining easier to see on x-ray. These tests are sometimes useful in diagnosing GI tumors, but they can miss some small intestine tumors.
You will probably have to fast starting the night before the test. If the colon is being examined, you may need to take laxatives and/or enemas to clean out the bowel the night before or the morning of the exam.
Barium swallow: This test (also known as an upper GI series) is used to look at the inner lining of the esophagus, stomach, and the first part of the small intestine. Patients getting this test drink a barium solution before the x-ray pictures are taken.
Small bowel follow through: This is a continuation of the barium swallow test that is sometimes used to look for problems in the small intestine. For this test, x-rays are taken at regular intervals over the course of a few hours as the barium passes through the intestines.
Enteroclysis: This test is another way to look at the small intestine. A thin tube is passed through the mouth or nose, down the esophagus, and through the stomach into the start of the small intestine. Barium is sent through the tube, along with a substance that creates more air in the intestines, causing them to expand. X-rays of the intestines are then taken. This test can give better images of the small intestine than a small bowel follow through, but it is also more uncomfortable.
Barium enema: This test (also known as a lower GI series) is used to look at the inner surface of the large intestine. For this test, the barium solution is given through a small, flexible tube inserted in the anus while the patient is lying on the x-ray table. When the colon is about half full of barium, the patient rolls over so the barium spreads throughout the colon. For a regular barium enema, x-rays are then taken. After the barium is put in the colon, air may be blown in to help push the barium toward the wall of the colon and better coat the inner surface. Then x-rays are taken. This is called an air-contrast barium enema (also known as double-contrast barium enema).
Barium x-rays are used less these days than before. In many cases they are being replaced by endoscopy – where the doctor actually looks into the colon or stomach with a narrow fiber optic scope (see below).
Computed tomography (CT) scan
The CT scan is an x-ray test that produces detailed, cross-sectional images of your body. Instead of taking one picture, like a standard x-ray, a CT scanner takes many pictures as it rotates around you. A computer then combines these into images of slices of the part of your body that is being studied. Unlike a regular x-ray, a CT scan creates images of the soft tissues in the body.
Before any pictures are taken, you may be asked to swallow an oral contrast liquid. This helps outline your digestive tract to make tumors easier to see. You may also receive an intravenous (IV) line so that a dye (contrast) can be injected. This can help better outline structures in your body.
The injection can cause some flushing (redness and warm feeling, especially in the face). Some people are allergic and get hives or, rarely, more serious reactions like trouble breathing and low blood pressure. Medicines can be given to prevent and treat any allergic reactions, so it is important for you to let the doctor know before the scan about any allergies or previous reactions you might have had to contrast material used for x-rays.
CT scans take longer than regular x-rays. You need to lie still on a table while they are being done. During the test, the table slides in and out of the scanner, a ring-shaped machine that completely surrounds the table. The test is painless, but you may find it uncomfortable to hold still in certain positions for minutes at a time. Spiral CT (also known as helical CT) is now used in many medical centers. This type of CT scan uses a faster machine that reduces the dose of radiation and yields more detailed pictures.
CT scans can be useful in patients with GISTs to find the location and size of a tumor, as well as to see whether it has spread into the abdomen or the liver.
In some cases, CT scans can also be used to guide a biopsy needle precisely into a suspected cancer or metastatic lesion. However, because this can be risky when a GIST is involved (bleeding, possible increased risk of tumor spread), these types of biopsies are usually done only if the result might affect the decision on treatment. (For more information, see the information about biopsy below.)
Magnetic resonance imaging (MRI) scan
MRI scans use radio waves and strong magnets instead of x-rays. The energy from the radio waves is absorbed and then released in a pattern formed by the type of tissue and by certain diseases. A computer translates the pattern into a very detailed image of parts of the body. A contrast material might be injected just as with CT scans, but is used less often.
MRI scans are a little more uncomfortable than CT scans. They take longer – often up to an hour. You have to lie inside a narrow tube, which is confining and can upset some people with a fear of enclosed spaces (claustrophobia). Newer, "open" MRI machines can help with this, but they are less available. The machine also makes buzzing and clicking noises that some people might find disturbing. Some places will provide ear plugs to block this noise out.
MRI scans can sometimes be useful in people GISTs to help find the extent of the cancer in the abdomen, but usually CT scans are enough. MRIs are also useful in looking for return of cancer (recurrence) or spread (metastases) to distant organs, particularly in the brain or spine.
Positron emission tomography (PET) scan
For a PET scan, a radioactive substance (usually a type of sugar related to glucose, known as FDG) is injected into the blood. The amount of radioactivity used is very low. Because cancer cells in the body are growing quickly, they absorb large amounts of the radioactive sugar. A special camera can then create a picture of areas of radioactivity in the body.
PET scan images are not finely detailed like CT or MRI images, but a PET scan can look for possible areas of cancer spread in all areas of the body at once. Some newer machines are able to perform both a PET and CT scan at the same time (PET/CT scan). This lets the doctor see areas that "light up" on the PET scan in more detail.
PET scans can be useful tests for looking at GISTs, especially if the results of CT or MRI scans aren't clear. This test can be used to look for possible areas of cancer spread to help determine if surgery is an option.
PET scans can also be helpful in finding out if a drug treatment is working, as they can usually give an answer quicker than CT or MRI scans. The scan is usually obtained about 4 weeks after starting the medication. If the drug is working, the tumor will stop taking up the radioactive sugar. If the tumor still takes up the sugar, your doctor may decide to change your drug treatment.
Endoscopy
These tests use a flexible lighted tube (endoscope) with a tiny video camera on the end. The camera sends pictures to a video screen, so that the doctor can clearly see any masses (tumors) in the lining of the digestive tract. If abnormal areas are found, small pieces of tissue can be removed (biopsied) through the endoscope. The biopsy sample can be looked at under the microscope to find out if cancer is present and what kind of cancer it is.
When looking into the GI tract with an endoscope, the doctor may see only a bulge under the normally smooth surface if a GIST is present. This is because GIST tumors are often below the lining (mucosa) of the GI tract. This makes them harder to see with endoscopy than more common GI tract tumors, which typically start in the mucosa. GISTs that are below the mucosa are also harder to biopsy through the endoscope. This is one reason why only about half of GISTs are diagnosed before surgery.
If the tumor breaks through the inner lining of the GI tract and is easy to see on endoscopy, there is a greater chance that the GIST is cancerous (malignant).
Upper endoscopy (esophagogastroduodenoscopy or EGD)
For this procedure, patients are given medicines to make them sleepy (sedated). Then the endoscope is passed down through the mouth to look at the inner lining of the esophagus, stomach, and first part of the small intestine. Biopsy samples may be taken from any abnormal areas
Colonoscopy (lower endoscopy)
For this test, a type of endoscope known as a colonoscope is inserted through the anus and up into the colon. This lets the doctor look at the lining of the entire rectum and colon at to take biopsy samples from any abnormal areas.
To get a good look at the inside of the colon, it must be empty and cleaned out before the test. This often means using a strong laxative the night before. Sometimes enemas are also needed the morning of the procedure to make sure the bowels are empty.
You will be given intravenous (IV; into a vein) medicine to make you feel relaxed and sleepy during the procedure. A colonoscopy may be done in a hospital outpatient department, in a clinic, or in a doctor's office. It usually takes 15 to 30 minutes, but it may take longer if a tumor is seen and/or a biopsy taken.
Capsule endoscopy
Unfortunately, neither upper nor lower endoscopy can reach all areas of the small intestine. Capsule endoscopy is one way to look at the small intestine.
This procedure does not actually use an endoscope. Instead, the patient swallows a capsule (about the size of a large vitamin pill) that contains a light source and a very small camera. Like any other pill, the capsule goes through the stomach and into the small intestine. As it travels (usually over the course of about 8 hours), it takes thousands of pictures. These images are transmitted electronically to a device worn around the person's waist. The pictures can then be downloaded onto a computer, where the doctor can view them as a video. The capsule passes out of the body during a normal bowel movement and is discarded.
This test requires no sedation – the patient can just continue normal daily activities as the capsule travels through the GI tract. This technique is fairly new, and the best way to use it is still being studied. One disadvantage is that any abnormal areas seen can't be biopsied during the test.
Double balloon enteroscopy
This is another way to look at the small intestine. The small intestine is too long (20 feet) and has too many curves to be examined well with regular endoscopy. This method gets around these problems by using a special endoscope that is made up of 2 tubes, one inside the other.
The procedure is done after the patient is given drugs to make him or her relaxed, or even asleep. The endoscope is then inserted either through the mouth or the anus, depending on if there is a specific part of the small intestine to be examined.
First the inner tube, which is an endoscope, is advanced forward about a foot as the doctor looks at the lining of the intestine. Then a balloon on the end of the endoscope is inflated to anchor it. The outer tube is then pushed forward to near the end of the inner tube and is anchored in place with a second balloon. The first balloon is deflated and the endoscope is advanced again. This process keeps being repeated over and over, letting the doctor see the intestine a foot at a time. The test may take as long as 2 hours to complete.
This test may be done along with capsule endoscopy. The main advantage of this test over capsule endoscopy is that the doctor can take a biopsy if something abnormal is seen.
Endoscopic ultrasound
This is actually a type of imaging test that uses an endoscope. Ultrasound uses sound waves to take pictures of parts of the body. For most ultrasounds, the transducer (a probe that emits sound waves) is placed on the skin.
For an endoscopic ultrasound, the ultrasound probe is placed on the tip of an endoscope. This allows the probe to be placed very close to (or on top of) the tumor. Like a regular ultrasound, the probe gives off sound waves and then detects the echoes that bounce off tissues of the digestive tract wall. A computer then translates the pattern of echoes into an image of the area being looked at.
Endoscopic ultrasound can be used to find the precise location of the GIST and to determine its size. It is useful in finding out how deeply a tumor has grown into the wall of the digestive tract (esophagus, stomach, intestine, or rectum). The test can also help show whether the tumor has spread to lymph nodes or has started growing into other tissues nearby. In some cases it may be used to help guide a biopsy (see below).
Biopsy
Even if a mass is found on an imaging test such as a barium x-ray or CT scan, these tests cannot tell if the mass is a GIST, some other type of tumor (benign or cancerous), or some other condition (like an infection). The only way to know what it is for sure is to remove cells from the abnormal area and look at them under a microscope. This procedure is called a biopsy. There are several ways to take a sample from a GI tract tumor.
Endoscopic biopsy
Biopsy samples can be obtained through the endoscope. When a tumor is found, the doctor can operate a biopsy forceps (pincers or tongs) through the tube to take a small sample of the tumor. Even though the sample will be very small, doctors can usually make an accurate diagnosis. About half the time, the biopsy will not get the cancer because it grows underneath the lining of the intestine or stomach. (The biopsy forceps can't go deep enough.)
Bleeding from a GIST after a biopsy is rare but can be a serious problem. If this occurs, doctors can sometimes inject drugs that constrict blood vessels through the endoscope into the tumor to stop the bleeding.
Fine needle biopsy
In some cases, a biopsy sample is obtained with a thin, hollow needle. The most common way to do this is during an endoscopic ultrasound. The doctor uses the ultrasound image to guide a needle on the tip of the endoscope into the tumor. Less commonly, the doctor may place a needle through the skin and into the tumor while guided by an imaging test such as a CT scan.
These types of biopsies must be done carefully and are usually done only if they will help determine treatment options, because doctors are concerned they may cause bleeding or possibly increase the risk of cancer spreading.
Surgical biopsy
If a sample can't be obtained from an endoscopic or needle biopsy or if the result wouldn't affect treatment options, a doctor may recommend waiting until surgery to remove the tumor to get a sample of it. The surgery is often done through an incision in the abdomen, (called a laparotomy). In some cases, small tumors can be removed using long, thin surgical instruments that are passed through a few smaller incisions in the abdomen. This is known as laparoscopic surgery, or keyhole surgery.
Testing the biopsy sample
Once a tumor sample is obtained, a doctor who specializes in lab tests (a pathologist) looks at it under a microscope. A pathologist may suspect that a tumor is a GIST, but he or she often can't be sure without further tests.
For a special test called immunohistochemistry, a part of the sample is treated with manmade antibodies that will attach only to the KIT protein (also called CD117). The antibodies cause color changes if the KIT protein is present, which can be seen under a microscope. Because most GIST cells contain this protein but cells of most other types of cancer do not, this test can be useful in determining whether a GI tumor is a GIST or not. If the tumor cells do not contain KIT, they will be checked to see if they have too much of the PDGFRA protein. This is found in about 5% of GISTs.
If the doctor is still unsure if the tumor is a GIST, he or she may do other tests on the biopsy sample to look for mutations in the c-kit or PDGFRA genes themselves.
If a GIST is diagnosed, the doctor will also look at the cancer cells in the sample to see how many of them are actively dividing into new cells. This is known as the mitotic rate. A low mitotic rate means the cancer cells are growing and dividing slowly, while a high rate means they are growing quickly. The mitotic rate is an important part of the stage of the cancer (see "How are gastrointestinal stromal tumors staged?").
Blood tests
Your doctor may order some blood tests if he or she thinks you may have a GIST. There are no blood tests that can tell if a person has a GIST. These tumors do not release any known substances in the blood that can be used to diagnose a GIST or to measure its response to treatment.
However, blood tests can sometimes point to a possible tumor (or to its spread). For example, a blood count can tell if you are anemic (have a low red blood cell count). Some people with GIST may become anemic because of bleeding from the tumor. Abnormal liver function tests may mean that the GIST has spread to your liver.
Blood tests are also done to check your overall health before you have surgery or while you get other treatments such as targeted therapy.
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