KIT+ GIST—Understanding the Basics
Understanding KIT+ GIST
GLEEVEC® is indicated to treat patients diagnosed with KIT–positive gastrointestinal stromal tumors (KIT+ GIST), an uncommon type of cancer found in the gastrointestinal (GI) tract.
Most GISTs grow in the stomach or small intestine, but some may form in the esophagus, large intestine, and anus. The risk factors for GIST are unknown, but heredity is rare.
- 50%–70% of GISTs occur in stomach
- 20%–30% of GISTs occur in small intestine
- Can also occur in esophagus, large intestine, and anus
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Cause of KIT+ GIST
The exact cause of KIT+ GIST is unknown, but doctors believe that a genetic mutation causes the unregulated growth of special cells found in the wall of the GI tract called interstitial cells of Cajal (ICCs). These special cells send signals that cause muscles to contract and slowly move food and liquid down the GI tract.
Most GISTs are caused by a mutation to the c-kit gene. This gene produces a protein called KIT, which causes cells to grow and divide. Normally the c-kit gene is only active when the body needs to produce more ICCs, but in KIT+ GIST, the gene is always signaling the body to constantly produce abnormal cells with the KIT protein. If these ICCs are constantly growing and dividing, this may explain why tumors form. Blocking the signal may eliminate or reduce abnormal cells and stop the body from making more.
Some GISTs are caused by a different genetic mutation, which causes the overproduction of the protein called platelet-derived growth factor receptor alpha (PDGFRα). Like the abnormal c-kit gene, this mutation may also cause the formation of gastrointestinal stromal tumors.
Both the KIT and PDGFRα proteins act as enzymes called tyrosine kinases. This is important because GLEEVEC is a type of drug called a tyrosine kinase inhibitor (TKI), but GLEEVEC is not indicated to treat GIST caused by PDGFRα.
Types of KIT+ GIST
It's important to know that all KIT+ GISTs have the potential to be malignant. KIT+ GIST, specifically, may be diagnosed as either localized or metastatic. If you have localized KIT+ GIST, this means that the tumor has not grown or spread to other areas of the body. For localized tumors, surgical resection—or removal of the tumor—is the first approach. Tumors in their original site are called primary tumors.
When a localized tumor grows and spreads to other areas of the body, it's called metastatic. If a localized tumor is removed and it comes back, it's considered metastatic. Whether you have localized or metastatic KIT+ GIST, it's important to partner with your healthcare team to get the best possible care.