What is GIST?
GIST is a tumor that usually arises in the tissue of the stomach or small intestine, or less often in the large intestine, esophagus or rectum. GISTs can be cancerous. There are approximately 6,000 cases of GIST per year in the United States, and GISTs tend to occur most frequently in those between the ages of 40-80 years old.
What are the symptoms?
Some patients have no symptoms and their tumors are found accidentally. For example, some tumors may be found when having testing or surgery for another reason. However, some people may experience symptoms such as abdominal pain and/or bloating, bleeding from the bowel, decreased appetite, and/or tiredness.
What causes GIST?
The exact cause of GIST is unknown. However, 95% of patients with GIST have a protein called Kit (CD 117) that has become abnormal, which then causes normal cells to grow faster and become cancerous.
How is GIST Diagnosed?
Your cancer doctor will obtain a history and physical exam and blood work. An upper endoscopy may be ordered to locate the tumor and/or to obtain a biopsy or piece of the tumor. An endoscopy is a test in which a tube with a camera at the end is placed into the mouth and passed through the esophagus, or food pipe, and into the stomach that allows the doctor to look for a tumor. A computed tomography (CT) scan of the abdomen and pelvis will also be obtained to understand where the tumor is and what size it is. This will also help the cancer doctor decide if the tumor can be removed (or so called "resectable"). In some instances a positron emission tomography (PET) scan will be performed as well to be sure the tumor is truly localized and resectable.
If the tumor appears to be localized and the surgeon can take out the entire tumor safely, then surgery will be performed. A pathologist studies the tumor under a microscope. The pathologist can then tell if the tumor is a GIST. He/she will also be able to test the tumor for Kit (CD 117).
Sometimes, the tumor is large or has spread and cannot be removed successfully. When this is the case, a biopsy is performed. A biopsy is a procedure that involves using a needle or surgical procedure to remove a part of the tumor. A pathologist then studies this tissue and he/she can usually tell if it is a GIST and check for Kit (CD 117).
How is GIST Staged?
There is no standard staging system for GIST. However, your cancer doctor will consider the size of the tumor, where it's located, whether it has spread, and how fast the tumor is dividing (mitoses) to determine how to treat the GIST and to help predict outcomes.
For example, a small tumor that is localized (has not spread) would be considered a low-risk tumor. This tumor would likely be cured by surgery. Other tumors may be considered intermediate or high risk.
What are the treatment options?
As mentioned above, some GISTs are cured by surgery. However, some tumors are too large or have spread to other areas where surgery would not be curative. In these situations, a medication called imatinib (Gleevec) would likely be prescribed. This is a pill taken once or twice daily by mouth. It works by attaching to KIT and blocking its ability to let cancer cells grow. This medication can either shrink the tumor or at least keep it from growing in about 85% of patients. Sometimes, if the tumor shrinks enough, surgery may become a treatment option. Unfortunately, the tumor eventually becomes resistant to imatinib and may start to grow again. Currently, there are new medications being studied in clinical trials, such as SU11248, for patients whose tumor becomes resistant to treatment with imatinib.
Overall, imatinib is usually tolerated well. However, some of the most common side effects include: nausea, diarrhea, swelling or puffiness around the eyes, rash, low blood counts (white and red blood cells) and fatigue. Imatinib may also cause tumors to bleed.
Whether imatinib (Gleevec) or other medicines can prevent a GIST from coming back after it is removed surgically has not yet been proven, but studies to investigate this possibility are underway.
Whether one receives surgery or treatment with medication, your doctor will likely have you get CT scans approximately every 3-6 months to monitor your condition. Sometimes, PET scans are done to assess the response to treatment.