GIST: Frequently Asked Questions
What is GIST?
GIST is a rare tumor of the GI tract. It most commonly affects the stomach, although it can develop in any part of the digestive system.
GIST is a soft tissue sarcoma. Most cancers are carcinomas. What’s the difference?
- Carcinomas start in the cells that cover the lining of the skin and organs (epithelial cells). Most stomach and colon cancers are carcinomas. Skin cancer is another type of carcinoma.
- Soft tissue sarcomas start in the cells of the connective tissues like cartilage, fat, nerves, and muscle.
More specifically, GIST starts in nervous system cells in the wall of the GI tract -- called interstitial cells of Cajal (ICCs). These cells send signals to the muscles in the digestive system to contract to move food and liquid through the system.
GIST is also different than many other tumors in how it progresses. All GIST tumors are malignant. However, chemotherapy and/or radiation are not effective for GIST.
What causes GIST?
GIST is caused by a genetic mutation, an error in the normal order of genes. In most cases, the mutation is to a gene that directs the cells to make a protein (called KIT or CD117) that causes the cells to grow and divide. In this case, the gene mutation causes the ICC cells to grow and divide in an uncontrolled manner, leading to a tumor.
There are no known risk factors for the development of GIST.
What is mutation testing?
Mutation testing may be done on the cancer cells to identify the exact genetic mutation that exists. This helps doctors understand how the cancer may behave and aid in guiding treatment.
At this time, mutation testing is recommended for everyone with GIST. Testing for the Kit mutation will be positive in 87% of cases of GIST. Testing for the PDGFRA genetic mutation will be positive in 4% of GIST cases.
How is this cancer staged?
Doctors use staging to determine the extent of a malignancy. These three factors determine staging:
- The size and location of the tumor
- Whether or not cancer has spread to lymph nodes or other organs
- How fast the cells are growing
The chart below shows how letters and numbers are used to identify your cancer stage. This information helps guide your treatment and prognosis.
|Letter||What it refers to|
|T||Size of the tumor (1 – 4)|
|N||Indicates whether it has spread to nearby lymph nodes (rare for GIST) most GISTS will be “N0” (zero).|
|M||Indicates whether the cancer has spread to nearby organs. (0 or 1)|
|Mitotic rate||How fast the cancer is growing (low or high)|
Do I need to see a specialist?
Because GIST is rare and can be unpredictable, choosing the correct doctor is an important decision. There are a limited number of doctors and medical centers experienced in treating GIST. Talk to your doctor about finding a doctor who is skilled in GIST treatment.