Your GIST Treatment Guide
What Are GIST Targeted Therapies? continued...
Gleevec is a “targeted therapy,” known as a tyrosine kinase inhibitor (TKI). These drugs interfere with the signals sent out by cancer cells, specifically those with the KIT mutation.
“Most people tolerate Gleevec very well,” says Demetri. However, as with all medications, there are side effects. The most common side effects of imatinib include:
- Fluid retention
- Swelling around the eyes and legs
- Diarrhea, nausea, and vomiting
- Muscle cramps
- Muscle or bone pain
- Abdominal pain
- Excessive gas
Some patients cannot tolerate imatinib and have to discontinue the drug. The most serious side effect -- severe liver dysfunction -- may result in the withdrawal therapy.
In this case, or for tumor recurrence or resistance during imatinib therapy, the drug sunitinib (Sutent) is used. This drug has a GIST control rate of more than 50% with 2-year survival rates.
“Sutent targets a different genetic signaling switch than Gleevec does, so it has different toxicities. You don’t get the swelling you see with Gleevec, but instead you get others, like mouth sores and change in taste, and most commonly high blood pressure, which doctors will need to monitor closely,” says Demetri.
The drug regorafenib (Stivarga) is used to treat patients who have tumors that cannot be surgically removed and no longer respond to other GIST treatments.
Other agents being evaluated for GIST include sorafenib (Nexavar), dasatinib (Sprycel) and nilotinib (Tasigna).
Is GIST Treatment Working?
With most cancers, doctors measure whether or not a treatment is working with one main yardstick: is the tumor shrinking, growing, or staying the same? If the tumor isn’t growing, or is even getting smaller, that’s a sign that the treatment is effective. When a tumor grows while a patient is on a certain drug, doctors will usually stop that drug since it isn’t controlling the cancer.
GIST is different. In the metastatic setting, when GIST is evaluated by CT scan or MRI scan to check treatment response, tumors may enlarge, or stay the same size, even though the patient is improving. A PET scan can help in these cases because they show tumor activity instead of tumor size. This fact is unique to GIST.
Treatments You Probably Won’t Need
Chemotherapy and/or radiation are not appropriate for use in GIST, although radiation may be used to control bleeding from a GIST tumor.
What Happens if the Cancer Spreads?
For some people diagnosed with GIST, the disease has already metastasized at the time of initial diagnosis. Metastasis is defined as tumor spread outside of the primary tumor site. If GIST comes back after treatment at its original site, it is known as local recurrence. Metastatic disease cannot be removed surgically, but a localized recurrence may be able to be surgically removed.