Gastrointestinal Stromal Tumors (GIST)

As previously stated, most GISTs occur in the stomach or small intestine. These tumors often grow into empty space inside the GI tract so they may not cause symptoms until they reach a certain size or are in a certain location. As a result, a small tumor may not cause any symptoms and may be accidentally found by the doctor. These types of GISTs tend to grow slowly.

Sometimes GISTs are found because they cause bleeding into the GI tract. Signs and symptoms of bleeding depend on where the bleeding tumor is located and how fast it is bleeding. If a GIST is bleeding more quickly, signs include throwing up bright red or dark blood, or bleeding into the stool. If a GIST is bleeding slowly over a long period of time, you may not experience throwing up blood or changes in stool. Rather, slow bleeding can lead to a low red blood cell count, making a person feel tired and weak.

Other possible symptoms of GIST include: abdominal pain, a noticeable mass or swelling in the abdomen, nausea or vomiting, loss of appetite and weight loss, and feeling full after eating small amounts of food.

Doctors use many tests to find and diagnose cancer. GISTs are diagnosed from physical exam and history, imaging, biopsy of abnormal areas, and laboratory tests.

• Physical exam and history
• Imaging: used to diagnose and to monitor GIST. Imaging used in GIST includes cComputed tomography (CT or CAT scan), eEndoscopy/endoscopic ultrasound (EUS), and mMagnetic resonance imaging (MRI).

Computed tomography (CT or CAT): takes pictures from inside of the body using x-rays taken from different angles. Images are combined to a detailed, 3D image to show abnormalities or tumors. CT scan can be used to measure tumor size or help see if cancer has spread to other body parts

Endoscopy/endoscopic ultrasound: used to see inside of the stomach or large bowel. A thin, lighted tube is inserted into the GI tract and if abnormal areas are found, a sample of tissue can be removed (see biopsy below) to check for evidence of cancer

MRI (Magnetic resonance imaging): uses magnetic fields, not x-rays, to produce detailed images of the body and can be used to measure a tumor’s size

• Biopsy: if something abnormal is found on imaging, the doctor will order a biopsy of the abnormal area. The reason for this is that even if something abnormal is seen on imaging, there is no way to tell if the abnormal area is GIST, other type of tumor, or some other condition such as an infection. The only way to know for sure is to remove cells from the area (this procedure is called a biopsy) and examine them under a microscope.

Once obtained by biopsy, a pathologist will look at the abnormal area under a microscope. Sometimes they can tell just by looking that the tumor is a GIST, but oftentimes further tests are ordered to be sure. These laboratory tests that can help to confirm a GIST diagnosis are immunohistochemistry (ICH), molecular genetic testing, and mitotic rate assessment.

Other Laboratory Tests:

• Immunohistochemistry (IHC) – Lab test looking to see if certain proteins are present in the biopsy. Some proteins most often tested if GIST is suspected are KIT, DOG, and PDGFRA. Most GIST cells have these proteins and most other cancer cell types do not, so this test can help tell if a GI tumor is a GIST or not.
• Molecular genetic testing-this test is done to look for mutations in the KIT or PDGFRA genes themselves, as most GIST cells have mutations in one or the other. Less frequently, tests may be done to look for other gene mutations, such as SDH.
• Mitotic rate – A measure of how fast the cancer cells are growing and dividing. A low rate means the cancer cells are dividing and growing slowly and a high rate means they are dividing and growing quickly. This can help the doctor determine which treatments are appropriate for individual GISTs.

Treatment options depend on a several factors, including the tumor size, the mitotic rate, where the tumor is located in the GI tract, the genetic makeup of the tumor, and if the tumor has spread to other parts of the body. Treatment options include surgery and targeted therapies.

• Surgery is the removal of the tumor and some surrounding healthy tissue during an operation. For patients with GIST that has not spread to other parts of the body, surgery is the standard treatment and should be performed when possible.
• Targeted therapy, such as tyrosine kinase inhibitors (TKIs). Targeted therapy is treatment that targets the GISTs specific genes or proteins that are causing it to grow and survive. The goal of this therapy is to block the growth and spread of the cancer while trying to limit damage to normal, healthy cells. Examples of FDA approved TKIs to treat GIST include Gleevec®, Sutent®, Stivarga®, Ayvakit™, and Qinlock®. TKIs may be used in certain patients after surgery to reduce the risk of GIST recurring (Gleevec®), and also in patients who have GIST that has spread to other parts of the body (metastatic disease).