After diagnosis and any surgery, patients with gastrointestinal stromal tumor (GIST) receive monitoring tests to:
a) evaluate bloodwork and other parameters for possible side effects from drugs such as imatinib (Gleevec) or sunitinib (Sutent)
b) look for disease recurrence, metastasis, or for changes in characteristics or size of unresected tumors.
For patients taking imatinib (Gleevec), bloodwork is done more frequently at the beginning of treatment (see Dr. Blanke's opinion) and at every oncology check-up later during treatment.
For patients taking sunitinib (Sutent) bloodwork is done at the beginning of each treatment cycle and may include additional serum chemistry tests in addition to those listed below.
Complete Blood Count
This includes measurements of:
- anemia indicators [hemoglobin, hematocrit]
- relative proportions of different types of blood cells [red blood cells (RBC), white blood cells (WBC), white blood cell differential (counting different types of white blood cells), platelets]
- other characteristics of the blood cells [MCV, MCH, MCHC, RDW]
Comprehensive Metabolic Panel
This includes tests for function of the:
- kidneys [blood urea nitrogen (BUN), creatinine],
- liver [albumin, total protein, bilirubin, alkaline phosphatase (ALP), alanine amino transferase (ALT, also called SGPT), aspartate amino transferase (AST, also called SGOT)].
If you want to read details about these tests, you can find a wealth of information at websites such as www.labtestsonline.com
Heart Function Tests
Blood pressure is normally measured at every office visit.
For patients taking sunitinib (Sutent) the following tests should be done at the beginning of each treatment cycle:
- monitoring of left ventricular ejection fraction (LVEF)
- monitoring of adrenal insufficiency.
Each patient's physician will select the most appropriate imaging tests to detect potential recurrence or tumor status changes for that individual. The frequency at which these studies are done depends on the accepted practice in the particular country concerned, as well as the length of time the patient has been followed. For routine monitoring the National Comprehensive Cancer Network (Soft Tissue Sarcoma Guidelines, 2006) recommends:
- for patients with surgical resection of GIST, scans every 3-6 months for 3-5 years and then annually
- for patients with metastatic or primary GIST, scans every 3-4 months.
Additional information about imaging techniques and photographs of the equipment used is available at www.radiology.com
One practical tip for scan days is to wear clothing with no metal parts (no metal zippers, snaps, or hooks) so that the patient can remain dressed and does not need to put on a hospital gown for the procedure. For example, an all-elastic sports bra and elastic-waist exercise apparel would be suitable. Wear loose sleeves or short sleeves to allow for easy insertion of the intravenous contrast.
Patients can request copies of their scans for their personal records. If you request this at the time of the scan, there may be no extra charge, or a smaller fee than if you make the request later. Many facilities can put a copy onto CD-ROM for you. Compared to the bulky and heavy film copies, CD-ROM copies are especially handy if you ever need to send your records to a distant medical facility, as they are easy to mail, and you can duplicate them yourself on a computer with a CD burner.
Computed Tomography (CT scan, CAT scan)
CT is the most commonly used imaging technique for GIST monitoring. CT machines take a series of X-ray images of the body, and each image shows a "slice." The slices are typically about one centimeter apart. For GIST, usually these slices are in a transverse plane (parallel to the top of the head), creating slices through the abdomen from the level of the chest to the pelvis. Sometimes the radiologist may decide to use another plane in addition, such as sagittal-plane slices from one side of the trunk to the other, parallel to the spine.
Patients are usually instructed not to eat during the 12 hours prior to a scan and not to drink within a few hours of the scan. Patients usually must drink a gastrointestinal (GI) contrast material once or twice during the 12 hours prior to the scan, but medical facilities differ in the type of contrast preferred. The purpose of this GI contrast is to coat the gastrointestinal (GI) tract so that any tumors inside the tract can be seen, as well as any tumors that have a small opening into the GI tract. Some facilities use barium-based contrast, while others use alternative types.
An injection of intravenous contrast is also used during the scan to illustrate the blood supply to tumors and to help in visualizing tumors as the circulation brings the contrast material to the tumor. Most intravenous contrast contains iodine, and some patients may have an allergic reaction to this. People who are allergic to shellfish are more likely to be allergic to iodine contrast. Allergic patients may be given prednisone or benadryl before the scan to prevent reactions. Non-iodine contrasts may be specified, or MRIs may be a better choice for allergic patients. Patients with poor kidney function should not be given the iodine contrast because of the load on the kidneys.
Very small tumors cannot be seen with CT. Small tumors arising from the small intestine, peritoneum, or mesentery are more difficult to visualize than those arising from the stomach. Liver tumors may be visible only with certain intravenous contrast conditions.
With modern machines, CT scans take only a few minutes to complete after the setup is done. Make sure to drink plenty of water after a scan to help flush contrasts from your system.
See Dr. Choi's article "Imaging GIST Response to Treatment" for more about CT results in GIST; check the free-access references at the end too.
Also see the CT page of GIST Support wiki.
Magnetic Resonance Imaging (MRI)
MRI uses strong electromagnetic radio waves to image the body by orienting protons in body tissues in an electromagnetic field. Because there is no ionizing radiation involved, patients do not accumulate radiation exposure from repeated scans. MRI produces very detailed images of soft tissues, making it especially useful for detection of liver metastases of GIST. The intravenous contrast for MRI is not iodine-based; therefore, it is not likely to cause allergic reactions. Some MRI machines place the patient in a tunnel-like space, which may bother people who tend toward claustrophobia. However, other MRI machines use an open ring rather than a tube. Note that doctors' opinions vary about the quality of images from tunnel versus ring MRI techniques; ask your physician about the clarity of images from your local providers.
People with metal implants (such as cardiac pacemakers, pins in joints, etc.) cannot be given MRI because of the magnetic field. Patients may not wear jewelry, watches, hearing aids, or any metal objects during the scan. MRI is somewhat more expensive than CT but is widely available. MRI takes about 30 minutes to complete. There are usually no limitations on food intake prior to MRI.
FDG-Positron Emission Tomography Imaging (PET scan)
A PET scan detects the uptake of a radioactive tracer (usually glucose) by different body tissues to identify areas with increased uptake. Tumors usually have increased tracer uptake compared to the standard uptake value of other tissues and therefore appear as "hot spots" on the PET scan. If drug treatment with imatinib (Gleevec) or sunitinib (Sutent) is successful in making a tumor quiescent, then the PET will "go cold," indicating that the treatment is working long before any reduction of tumor size becomes apparent on CT scanning.
Because PET scans are much more expensive and less widely available than CT scans, they are not used for routine monitoring outside of special clinical trials. Situations when PET may be used include:
- to detect metastases not apparent otherwise
- to detect an otherwise unknown primary tumor
- to determine rapidly whether a tumor is responding to a particular treatment (so that an alternative can be tried rapidly if there is no response)
- to clarify a suspicious area detected by CT or MRI, thereby avoiding an invasive procedure to investigate.
The patient must wait quietly for 60-90 minutes after injection of the tracer before the scan is given. The PET scan takes 30-45 minutes once it is begun.
Not all GISTs demonstrate increased uptake on PET at baseline (prior to treatment). For GISTs that are not "PET avid" this imaging technique is not useful.
For more information about PET used in monitoring GIST, see the free-access article "The lessons of GIST--PET and PET/CT: a new paradigm for imaging" by Annick van den Abeele, MD.
Also see our page about PET scans on our GIST Support wiki.
Combination PET/CT (fusion PET/CT)
A dual-purpose imaging device, PET/CT is literally the combination of PET (positron emission tomography) and CT (computed tomography) imaging techniques within a single machine. The individual scans, which are taken virtually simultaneously, can be presented separately or as a single, overlapping, or "fused" image. The two techniques present different types of information about the human body: PET shows metabolic or chemical activity in the body; CT shows the body's anatomical structures. For example, a PET scan would highlight a tumor's increased glucose consumption, while a CT scan would reveal its physical mass. Taking the two scans virtually simultaneously ensures that the patient remains in place and, therefore, that the two images form a precise computer overlay-that the tumor "hot spot" on the PET scan corresponds directly to the physical mass on the CT scan. This fused image provides a more reliable alternative to the traditional side-by-side visual comparison of PET and CT images.
Note that the CT images in a combination PET/CT are usually taken at wider "slice" intervals than in a dedicated CT. Therefore, size measurements of a tumor from one scan to the next may not be as useful for evaluating tumor size changes than would be true for sequential dedicated CT exams.
A well-illustrated, detailed tutorial about PET/CT is available at the website of the University of Virginia.
The website of Columbia University shows photos of a combination machine compared to stand-alone machines.
The website of Washington Imaging Services shows a picture of the combo machine, as well as discusses what to expect during and after the scan. Although the actual scan takes less than 40 minutes, a patient is usually in the clinic for about 90 minutes from beginning to end of a CT/PET fusion scan.