Your GIST Treatment Guide
Arnold Wax, MD
If you’ve been diagnosed with a gastrointestinal stromal tumor (GIST), there’s good news. GIST has become a treatable disease, thanks to advances in research and treatment over the last 15 years.
How Is GIST Treated?
The primary treatment for GIST is surgery. During surgery, the tumor is removed completely in approximately 85% of cases.
“More than half of all GIST tumors are small, not very aggressive, and easily removed during surgery,” says George Demetri, MD, associate professor of medicine at Harvard Medical School and director of the Center for Sarcoma and Bone Oncology at the Dana-Farber Cancer Institute and Brigham and Women's Hospital in Boston.
After surgery, experts study the tumor under a microscope to determine the proper diagnosis and the likelihood of the tumor recurring.
There are three main factors that help determine what kind of treatment you will have next:
- Tumor size. Tumors that are less than two centimeters in size are less likely to recur than larger tumors. The larger the tumor, the more likely it is to recur.
- The “mitotic index.” This is a measure of how many cells in the tumor are dividing. More dividing cells means a more aggressive tumor.
- Tumor location. GIST cancers that are found in the stomach are less likely to return than those found in the small intestine or the rectum.
The recurrence of GIST is most likely within the first two years after surgery. Therefore, monitoring is recommended at intervals of every 3-6 months, with CT scans. PET scans are not a substitute for CT scans.
What Are GIST Targeted Therapies?
For patients who have a more aggressive form of GIST and are at high risk of recurrence, the standard treatment is imatinib (Gleevec). This drug targets cells that have the C-KIT mutation, which is present in 87% of GIST tumors.
Gleevec has been shown to be effective in preventing GIST from recurring. In a study in which imatinib was given after surgery for high- risk GIST, one year of therapy was superior to no therapy after surgery.
A recent study that compared three years of imatinib after surgery to one year of therapy demonstrated superiority for the longer treatment. The FDA has now approved three years of postsurgical imatinib for GIST.
In certain circumstances, Gleevec may not be recommended after surgery. These circumstances may include KIT negative tumors (13%) or the presence of the PDGFRA gene (4%). In the latter instance, the PDGFRA gene conveys imatinib resistance, but also reduces the risk of GIST recurrence.
“There are different kinds of mutations in GIST tumor cells,” says Demetri. “About one out of five GISTs is driven primarily by something called the PDGFRA gene. This makes them resistant to Gleevec, so there’s no point to taking it. The good thing is that this mutation also makes the tumor act like a pussycat; it might be very big, but it rarely would come back. That’s why it’s important that your tumor cells undergo molecular testing, so that you don’t spend years on a treatment that won’t do anything for you.”