Diagnosis

After asking questions about your symptoms and medical history, your doctor will examine you carefully, checking for a growth in your abdomen. If signs and symptoms suggest that you may have a GIST, tests to locate it and then determine its likelihood of spreading (metastasizing) to other organs will follow. These tests may include:

• Contrast-enhanced computerized tomography (CT) scan. For this test, you swallow a liquid that makes your stomach and small intestine more visible on X-rays. You may also receive an injection of a similar substance. Then the scanner takes numerous X-rays as it moves over your abdomen. A computer combines the X-rays into detailed, cross-sectional images of your abdominal organs, showing the size and position of the tumor.
• Upper endoscopy. The doctor examines the inner lining of the esophagus, stomach and the first part of the small intestine with a flexible, lighted tube (endoscope) passed down through your mouth. It may be possible to take small samples of abnormal tissue during an upper endoscopy. During this test, you'll receive a mild relaxing medication (sedative) through an intravenous line.
• Endoscopic ultrasound (EUS). This test also uses an endoscope, but with an ultrasound probe on the tip of the scope. As sound waves from the probe create echoes that bounce back to the probe, a computer translates the echoes into an image of the structures in the abdomen, showing the precise location of the tumor. If the tumor has metastasized to your liver or the lining of your abdomen, these areas may also be visible. An EUS also helps determine the depth of the tumor within the wall of the stomach or other locations in the gastrointestinal tract.

• Fine-needle aspiration biopsy. A small sample of tissue from the tumor is necessary for a definite GIST diagnosis. The preferred method for taking a biopsy sample is endoscopic ultrasound with fine-needle aspiration. This procedure is the same as an EUS, but with a thin, hollow needle on the tip of the endoscope. The needle is used to remove small amounts of tissue for laboratory analysis.

  Sometimes these tests aren't possible, or their results are inconclusive, so a suspected GIST can't be located without surgery. Tissue analysis then takes place after the tumor is removed.

• Laboratory tests on biopsies. These tests provide information on the proteins tumor cells make. One of these tests, immunohistochemistry, detects specific proteins controlled by genes in GIST cells. Identification of these proteins helps guide treatment decisions. Sometimes, actual genetic testing of biopsy samples is necessary to locate GIST genes in tumor DNA. GIST cells are also examined under a microscope to see how many cells out of 50 different microscopic fields are actively dividing. This number is known as the mitotic rate. The higher the mitotic rate in a tumor, the more aggressive it is, and the greater is its likelihood of spreading to other organs.