A gastrointestinal stromal tumor (GIST) is a type of tumor that occurs in the gastrointestinal (GI or digestive) tract, including the esophagus, stomach, gallbladder, liver, small intestine, colon, rectum, and lining of the gut. GISTs are different from other types of gastrointestinal tumors because of the type of tissue in which they start.

Originally, GISTs were thought to be either muscle or nerve tumors, but recent research points to GISTs starting in cells found in the walls of the GI tract, called interstitial cells of Cajal (ICC); these cells send signals to the GI tract to help move food and liquid through the system.

GISTs belong to a group of cancers called soft tissue sarcoma. Soft tissue sarcomas are a group of cancers that develop in the tissues that support and connect the body, and the sarcoma cells resemble the cells that hold the body together, including fat cells, muscles, nerves, tendons, joints, blood vessels, or lymph vessels.

It is important to note that GISTs can be either benign or malignant. Sometimes it may be hard for the doctor to tell immediately whether a GIST is likely to come back after treatment. As a result, the doctor will look at many factors to determine the best treatment, including the size of the tumor, whether it has already spread, how many dividing cells there are, and the tumor’s location.

Because GIST cancers arise from the GI tract wall, they are usually attached to the outside of the involved organ, growing outward; this is sometimes referred to as exophytic. Occasionally a GIST may grow inward through the muscle layer of the GI tract wall and then develop partly inside the digestive tract lumen; this is sometimes called endophytic.

More than half of GISTs start in the stomach. Most of the remaining start in the small intestine, but GISTs can be found anywhere in the GI tract.

How common is GIST?

GIST is one of the not so common tumors Most primary care physicians and many pathologists and oncologists go through their entire professional careers without seeing a single GIST. This is important to patients because misdiagnosis can delay the start of appropriate treatment.

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.

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.

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).

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.

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.

Introduction

Prior to the introduction of targeted molecular drug therapies (starting with imatinib/Gleevec), surgery was the only useful treatment for GIST. Surgery is still the cornerstone of GIST treatment whenever resection is possible. Complete removal of a primary tumor is potentially curative, especially when the tumor is small and the risk classification is low.

What is the treatment of GIST?

Many years of treating patients and testing treatments in clinical trials has helped doctors know what is likely to work for a particular type and stage of tumor. You will be advised on the best treatment for you. This will depend on the type of tumor you have, where it is and how far it has spread and your general health.

Treatment options for people with GIST involve surgery and targerted therapy (Imatinib). Chemotherapy and radiation therapy have no role in treatment of GISTs.

Surgery is the main treatment for a gastrointestinal stromal tumor (GIST) that hasn’t spread is usually surgery. The goal of the surgery is to completely remove all of the cancer.

No matter what type of surgery is done, it is very important that it is done carefully by a surgeon with experience treating GISTs. GISTs are thought to be delicate tumors, and many doctors have voiced their concerns about bleeding and the possible increased risk of spreading the cancer if the capsule around the tumor is opened during surgery.

Targeted therapy

Targeted therapy is a treatment that targets specific genes, proteins, or the tissue environment that contributes to cancer growth and survival. In 2002, the U.S. Food and Drug Administration (FDA) approved imatinib (Gleevec) for the treatment of GIST. Imatinib is a tyrosine kinase inhibitor, and it is the drug of choice in treating GIST. Since this drug has become available, the prognosis for patients with GIST has improved considerably. It is usually given as either the only treatment or in combination with surgery (before or after surgery).

The usual dose of imatinib is 400 milligrams (mg) daily. In some patients the dose can be raised to 800 mg daily.

Sunitinib (Sutent), like imatinib, is a tyrosine kinase inhibitor called an anti-angiogenic that stops tumors from creating new blood vessels. It was approved in 2006 by the FDA for treating GIST when the tumor continues to grow even after treatment with imatinib, or when imatinib cannot be given.