What are the tests carried out to diagnose GIST?
This section lists common tests for the cancers. It is not necessary for all the tests to be performed for a patient. Your doctor will select the tests that will assist him / her to have the maximum information about the tumor/ disease. Before referring you for tests, your doctor will take a full medical history and examine you. You may also have a blood test and chest x-ray to check your general health.
Computerised tomography (CT) scan
A CT scan is a type of x-ray that gives a picture of organs and other structures (including any tumours) in your body. It is used to see more details of a cancer and its relation to the surrounding organs in your body. It also gives information related to cancer spread into the lymph nodes, liver or lungs.
Endoscopy / Gastroscopy
In this test, a thin, flexible ‘telescope’ (called an endoscope) will be passed down your throat so that the doctor can examine your oesophagus, stomach and the upper part of your bowel. If anything unusual is seen, the doctor can put instruments down the endoscope and remove tissue to examine under a microscope (biopsy).
Endoscopic ultrasound scan (EUS)
This is similar to having an endoscopy and may be occasionally for people who may have stomach GIST. For this test, the endoscope has a small ultrasound probe on the end for more detailed information about the local spread of the tumor. It can help the doctor decide whether you should have some other modality of treatment before surgery.
Positron emission tomography (PET) scan
This test is combined with a CT scan by injecting a radioactive material in the body to highlight all areas where the tumor has or can spread. This test may be used to build up more information after an MRI or CT scan. PET-CT scan is not necessary for all patients. Your doctor will decide if you need to undergo this scan.
A biopsy is diagnosis made under a microscope by a pathologist using a small bit of tissue removed from a suspicious area or lump that is found to be abnormal.
Gastrointestinal stromal tumor (GIST) is a cancer that may be suspected from its appearance in imaging techniques such as CT scans, but the diagnosis can only be determined by a pathologist after examining tumor tissue from a biopsy, or from the entire tumor after it has been surgically removed (resected). The main role of the pathologist is to determine the type of tumor (diagnosis). This is done by judging the characteristics of tumor cells viewed under a microscope and the results from a series of tests. The pathologist also gives an opinion regarding the prognosis (the risk of recurrence or metastasis).
The pathologist selects and applies immunohistochemical tests (IHC studies) to tumor samples. These tests involve using antibodies to detect the presence of proteins that are expressed by the tumor cells. The pattern of proteins that are present or missing in a respective tumor in conjunction with the morphology of the tissue is taken into account for the final diagnosis.
The best immunostaining method for identifying GIST is to test for expression of KIT, also called CD117. Therefore, a positive result for KIT antibody testing is a strong indication of a GIST diagnosis.