Tests for Gastrointestinal Stromal Tumors

A CT scan combines many x-ray pictures to make detailed, cross-sectional images of the soft tissues of your body, such as the GI tract.

Before the test, you might get an IV (intravenous) injection and be asked to drink some contrast dye to help get clearer pictures.

CT scans can be useful in people who have or might have GISTs to find the location, size, and other characteristics of a tumor, as well as to see if it has spread to other parts of the body.

MRI scans create detailed images of soft tissues inside your body. This is done using radio waves and strong magnets instead of x-rays, so there is no radiation.

MRI scans can sometimes be useful in people with GISTs to help find the extent of the cancer in the abdomen, but usually, CT scans are enough. If a GIST is suspected in the rectum, MRI images might be better than a CT.

Ultrasounds use sound waves and their echoes to look inside the body.

Doctors can use a small ultrasound probe during an endoscopy exam, called endoscopic ultrasound (EUS), to look at a tumor and guide them during a procedure like a biopsy.

Before a diagnosis, an ultrasound of the abdomen might also be used to look for causes of abdominal pain.

A PET scan can be useful for looking at GISTs when they are first found, especially if the results of CT or MRI scans aren’t clear.

For a PET scan, a slightly radioactive form of sugar (known as FDG) is injected into the blood and collects mainly in cancer cells. These areas of radioactivity can be seen on a PET scan using a special camera. The pictures from a PET scan aren’t as detailed as CT or MRI images, but they can often show areas of cancer anywhere in the body. It can help determine if surgery is an option.

PET scans can also be helpful in finding out if treatment is working. The scan can be done again a few weeks after starting treatment. If the treatment is working, the tumor will stop showing up or appear less bright on the PET scan. If the tumor still takes up the sugar, your doctor might decide to change your treatment.

PET/CT scan: Many centers now have machines that can do 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.

X-rays can be used to see if the GI tract, which is a long tube, is blocked.

To do this, sometimes doctors will do a barium x-ray. In this procedure, a liquid containing a substance called barium is swallowed or placed in the upper or lower GI tract with a small tube, and a series of x-rays are taken.

Barium shows up bright white on the x-rays. If the barium cannot pass or is moving around a large object like a tumor, it can be seen on these x-rays.

Barium x-rays are not used as much as they were in the past. Today, CT/MRI scans and endoscopy are used more commonly.

For this procedure, an endoscope is passed through the mouth and down the throat to look at the inner lining of the esophagus, stomach, and first part of the small intestine. Biopsy samples might be taken from any abnormal areas.

Upper endoscopy can be done in a hospital, in an outpatient surgery center, or in a doctor’s office. This test is also known as an EGD (short for esophagogastroduodenoscopy).

You are typically given medicine through an IV to make you sleepy before the exam. The exam itself usually takes 10 to 30 minutes, but it might take longer if a tumor is seen or if biopsy samples are taken.

If medicine is given to make you sleepy, you will likely need someone you know to drive you home, not just a cab or rideshare service.

For colonoscopy, 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 inner lining of the rectum and colon and take biopsy samples from any abnormal areas.

To look inside the colon, it must be cleaned out before the test. Your doctor will give you specific instructions. You might need to follow a special diet for a day or more before the test. You might also have to take laxatives the evening before, which means you will spend a lot of time in the bathroom.

A colonoscopy can be done in a hospital, in an outpatient surgery center, or in a doctor’s office.

You will likely be given medicine through an IV to make you feel sleepy during the procedure. Less often, you might be given general anesthesia to put you into a deep sleep. The exam usually takes about 30 minutes, but it can take longer if a tumor is seen and/or a biopsy is taken.

Because medicine is given to make you sleepy, you will likely need someone you know to drive you home, not just a cab or rideshare service.

Neither upper endoscopy nor colonoscopy can reach all areas of the small intestine. Capsule endoscopy is one way to look at the entire small intestine.

In this procedure, you swallow a capsule, about the size of a large pill, that contains a light source and a very small camera. Like any other pill, the capsule goes through the stomach and into the intestines.

As it travels through the intestine, usually over about 8 hours, it takes thousands of pictures. These images are sent to a device worn around your waist. The pictures can then be downloaded onto a computer, where the doctor can view them.

The capsule passes out of the body during a normal bowel movement and is discarded.

This test requires no sedation – you can just continue normal daily activities as the capsule travels through the GI tract. One disadvantage of this test is that any abnormal areas seen can’t be biopsied during the test.

This is another way to look at the small intestine. The small intestine is too long and has too many curves to be examined well with regular endoscopy. But this method gets around these problems by using a special endoscope that is made of 2 tubes, one inside the other.

You are either given IV medicine to help you relax or general anesthesia that puts you into a deep sleep. The endoscope is then inserted either through the mouth or the anus, depending on which part of the small intestine needs to be examined.

Once inside the small intestine, the inner tube, which has the camera on the end, 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 is repeated, letting the doctor see the intestine a foot at a time. The test can take hours to complete.

This test might 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.

Like other forms of endoscopy, because you are given medicine to make you sleepy for the procedure, someone you know will likely need to drive you home, not just a cab or rideshare service.

Biopsy samples can be obtained through an endoscope. When a tumor is found, the doctor can insert 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 often make an accurate diagnosis. However, with GISTs, sometimes the biopsy forceps can’t go deep enough to reach the tumor because it's underneath the inner lining of the stomach or intestine.

Bleeding from a GIST after a biopsy is rare, but it can be a serious problem. If this occurs, doctors can sometimes inject drugs into the tumor through an endoscope to constrict blood vessels and stop the bleeding.

A biopsy can also be done using a thin, hollow needle to remove small samples of the area.

The most common way to do this is known as an endoscopic ultrasound-guided fine needle aspiration (EUS-FNA). The doctor uses an ultrasound (described above) to guide a needle on the tip of the endoscope into the tumor.

Less often, doctors might place a needle through the skin into an abnormal area using images like a CT scan to guide them. This is called a percutaneous biopsy. This might be used to confirm that a tumor has spread beyond the GI tract.

If a sample can’t be obtained from an endoscopic or needle biopsy, or if the result of a biopsy wouldn’t affect treatment options, the doctor might recommend waiting until surgery to remove the tumor to get a sample of it.

If surgery is done through a large cut (incision) in the abdomen, it is called a laparotomy.

In a laparoscopic or keyhole surgery, the tumor can be sampled or small tumors can be removed through a small incision. The surgeon uses a thin, lighted tube called a laparoscope to let them see inside the belly.

For this test, a part of the sample is treated with man-made antibodies that will attach only to a certain protein in the cells. The antibodies cause color changes if the protein is present, which can be seen under a microscope.

Testing for changes in genes often associated with GIST tumors, like KIT, PDGFRA, or SDH, is often done. This can help tell if certain targeted therapy drugs are likely to be helpful in treating the cancer.

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 or mitotic index.

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 determining the stage of the cancer.