Gastrointestinal Stromal Tumor - GIST: Diagnosis

Approved by the Cancer.Net Editorial Board, 02/2020

ON THIS PAGE: You will find a list of common tests, procedures, and scans that doctors use to find the cause of a medical problem. Use the menu to see other pages.

Doctors use many tests to find, or diagnose, a GIST. Your doctor may consider these factors when choosing a diagnostic test:

  • The type of tumor suspected

  • Your signs and symptoms

  • Your age and general health

  • The results of earlier medical tests

In addition to a physical examination, the following tests may be used to diagnose GIST or determine the best treatment plan. Not all tests listed below will be used for every person.

  • Computed tomography (CT or CAT) scan. A CT scan is often the best test to diagnose and monitor a GIST. A CT scan takes pictures of the inside of the body using x-rays taken from different angles. A computer combines these pictures into a detailed, 3-dimensional image that shows any abnormalities or tumors. A CT scan can be used to measure the tumor’s size or help doctors determine whether the cancer has spread to the liver or gut lining. Sometimes, a special dye called a contrast medium is given before the scan to provide better detail on the image. This dye can be injected into a patient’s vein or given as a pill or liquid to swallow.

  • Endoscopy/endoscopic ultrasound. An endoscopy allows the doctor to see the inside of the stomach or large bowel. The patient may be sedated. Sedation is giving medication to make a patient more relaxed, calm, or sleepy. With an upper endoscopy, the doctor inserts a thin, lighted tube called a gastroscope through the mouth, down the esophagus, and into the stomach and upper small bowel. With lower endoscopy, the scope is inserted through the anus to visually evaluate the rectum and colon. If abnormal areas are found, the doctor can remove a sample of tissue and check it for evidence of cancer (see "Biopsy," below). A special type of test called a capsule endoscopy involves swallowing a small camera. This allows very clear viewing of the small intestine. It is rarely used but can be useful when other diagnostic methods are unable to find the cause of GI bleeding.

    An endoscopic ultrasound is similar to an endoscopy, but the scope has a small ultrasound probe on the end. The probe uses sound waves to create an image of the stomach or rectum and nearby organs. The ultrasound image helps doctors find out if or how far the cancer has spread into nearby tissues.

  • Magnetic resonance imaging (MRI). An MRI uses magnetic fields, not x-rays, to produce detailed images of the body. MRI can be used to measure the tumor’s size. A special dye called a contrast medium is given before the scan to create a clearer picture. This dye can be injected into a patient’s vein or given as a pill or liquid to swallow.

If a tumor (also called a mass or nodule) is found, the doctor will also do tests to learn if it is cancerous. For most types of tumors, a biopsy is the only sure way for the doctor to know if an area of the body has cancer. If a biopsy is not possible, the doctor may suggest other tests that will help make a diagnosis.

  • Biopsy. Your doctor may recommend a biopsy if a mass suspected of being a GIST is found. A biopsy is the removal of a small amount of tissue for examination under a microscope. The type of biopsy performed will depend on the location of the tumor. Other tests can suggest that a tumor is present, but only a biopsy can make a definite diagnosis. A pathologist then analyzes the sample. A pathologist is a doctor who specializes in interpreting laboratory tests and evaluating cells, tissues, and organs to diagnose disease.

    Based on the results of imaging scans, your doctor may recommend a biopsy or surgery. That’s because a single biopsy does not always diagnose a GIST. A patient may need surgery to remove the entire tumor and biopsies done in several locations of the tumor to make a diagnosis. However, it is very important that you see a team of medical and surgical oncologists experienced in treating GIST before a big surgery.

  • Tumor pathology. A pathologist makes a diagnosis of GIST by looking at the shape and appearance of tumor cells, doing tests for a protein called KIT and other tumor markers, and finding the mitotic count (a way of measuring how many cells are actively dividing; see Stages for more information).

  • Molecular testing of the tumor. Your doctor or pathologist may recommend running additional laboratory tests on a tumor sample to identify specific genes, proteins, and other factors unique to the tumor. Results of these tests can help determine your treatment options.

    GIST most often develops because of genetic mutations, or changes. This includes non-hereditary tumors. The 2 most common affected genes in GIST are called KIT and platelet-derived growth factor receptor alpha (PDGFRA). A tumor may have 1 of several different mutations to these genes, some of which are more harmful than others. Different mutations have different prognoses. Prognosis is the chance of recovery. When a tumor does not have a mutation in any gene that is tested for, it is called “wild type” (WT).Researchers are finding more mutations thought to cause GIST that may be used to help choose a patient’s treatment options. A protein called succinate dehydrogenase (SDH) is 1 of them. Another is BRAF, a gene occasionally changed in people with other types of cancer, such as melanoma or colorectal cancer.The results of mutation testing may help your doctor make treatment recommendations. This could include what dose of a drug called imatinib (Gleevec, Glivec) to use, or whether no further treatment or a different drug is recommended. This is discussed more in the Types of Treatment section.

  • Positron emission tomography (PET) or PET-CT scan. A PET scan is usually combined with a CT scan (see above), called a PET-CT scan. However, you may hear your doctor refer to this procedure just as a PET scan. A PET scan is a way to create pictures of organs and tissues inside the body. A small amount of a radioactive sugar substance is injected into the patient’s body. This sugar substance is taken up by cells 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. Doctors may use PET scans to detect the amount of the sugar substance taken up by the tumor. This information helps measure how well the treatment is working because sometimes GIST tumors do not change in size even when treatment is working.

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

The next section in this guide is Stages. It explains the system doctors use to describe the extent of the disease. Use the menu to choose a different section to read in this guide.