Gastrointestinal Stromal Tumors are often diagnosed during routine tests for other more common conditions. To obtain more knowledge about the cause of a patient's symptoms, a doctor might conduct the following tests:

• Upper endoscopy (inspection of organs or cavities using a device called endoscope)
• Laparoscopy (abdominal exploration using a device called a laparoscope)
• Colonoscopy (examination of the lining of the entire rectum and colon)
• Barium X-rays (helps find abnormalities of the lining of the esophagus, stomach and intestines)
• Ultrasound (using sound waves to take images of internal organs)
• Computed Tomography (CT or CAT) scan (a radiographic technique that produces a film that represents a detailed cross section of tissue structure)
• Magnetic Resonance Imaging (MRI) (another medical imaging technique)
• Positron Emission Tomography (PET) (another medical imaging technique)

These tests help determine whether patients have a tumor or tumors, where the tumor or tumors are located, how big they are, and whether or not the cancer has spread outside of the GI system (metastasized).

If a tumor is present, a tissue sample, or biopsy, is needed for the doctor to determine whether it is malignant (cancerous) or benign (non-cancerous), and to determine what type of cancer it is. If the tumor is a sarcoma, further testing of the tissue will determine the type of sarcoma and how rapidly the disease is likely to spread.

After the biopsy, the tumor sample is sent to a specialist called a pathologist who examines the cells and tissues. The pathologist will also test the tumor sample for the presence of Kit/CD117 - the enzyme thought to be responsible for most GISTs.

Prognostic Factors

Important factors include the size of the tumor, its grade and whether it has already shown signs of spread in the abdomen.

Doctors often use these factors to separate patients into very low-, low-, intermediate- and high-risk groups. These groupings describe the risk of the cancer spreading to distant areas in the body.

Whether or not a tumor has already spread to other areas at the time it is found is an important factor in determining outlook. It may have an effect on whether certain cancer treatment options, such as surgery, are available.

When these tumors are cancerous and spread away from the initial (primary) site, they most often spread within the abdomen, and in particular, to the liver. Less often, they may also spread to the lungs and bone. Spread to the lymph nodes, brain and elsewhere is not common. About half the time, the tumor is still localized when it is found; one fourth of the time it has spread to nearby tissues and one fourth of the time it has spread to distant sites.

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