A gastrointestinal stromal tumor (GIST) is a rare type of tumor that develops in the gastrointestinal (GI) tract. GISTs develop in a specialized type of cell in the GI tract, known as interstitial cells of Cajal (ICCs), or their precursor stem cells which differentiate to become ICCs.
The interstitial cells of Cajal are known as the GI pacemaker cells because they initiate and coordinate the muscle contraction required to move food and liquids through the esophagus into the stomach and bowels until the waste is eliminated from the body. ICCs are present throughout the GI tract.
Tumors are growths or lesions that form when abnormal cells multiply without control. Tumor cells develop the ability to evade programmed cell death (apoptosis), a natural part of the cell cycle, and continue to grow and divide.
Most GISTs develop in the stomach or small intestines, but can occur anywhere in the GI tract, such as the esophagus, colon, or rectum. In rare cases, GISTs can occur in the surrounding areas such as the fatty tissue (omentum) that lies over the abdominal organs, or the membrane (peritoneum) that envelops them.
Most people with GIST typically have a solitary tumor, but people with a family history of GIST may have multiple tumors. Some people with GIST may also develop a skin condition known as urticaria pigmentosa, with raised patches of skin that can hurt or itch when touched.
GISTs account for less than 1% of all gastrointestinal tumors. GISTs may be benign, or malignant (metastatic) growths that spread to other parts of the body. GISTs are more common in people older than 50 years, but rarely, they can occur in children and young adults.
What are the symptoms of GIST tumor?
Small GISTs may produce no symptoms and are often detected during tests for other reasons. Symptoms depend on the size and location of the GIST. Most GIST symptoms are secondary to GI blockage caused by large GISTs or bleeding from the tumor.
Symptoms of GIST related to blood loss may include:
Symptoms of obstruction caused by GIST may include
- Difficulty swallowing (dysphagia) if the GIST is in the esophagus
- Constipation with a colorectal GIST
- Jaundice with a GIST in the duodenum
General symptoms of GIST may include the following:
- Abdominal pain
- Nausea and vomiting
- Feeling full with very little food
- Loss of appetite
- Weight loss
- Rarely, a palpable mass or swelling in the abdomen
- Rarely, perforation in the GI tract caused by rupturing of a tumor, which is a medical emergency
To diagnose GIST, you may have to go through several tests and procedures such as:
- Blood tests
- Imaging tests
- Endoscopies and/or colonoscopies
What causes a GIST tumor?
Tumors are caused by a mutation in two types of genes, which lead to uncontrolled growth and division of cells:
- Proto-oncogenes: Genes that promote cell growth and proliferation, which are known as oncogenes when they mutate and develop the potential to cause cancer.
- Tumor suppressor genes: Genes that control growth, and repair damaged DNA or destroy cells with damaged DNA.
Most GIST tumors are caused by or related to mutations in one of the following oncogenes:
- KIT gene: The KIT gene encodes a protein known as CD117 which signals cells to grow and divide. The KIT gene is usually inactive in the ICCs once the GI tract development is complete. Mutations in KIT keep the gene active and cause GIST. More than 90% of GISTs have the KIT mutation.
- PDGFRA gene: PDGFRA gene also promotes cell growth and division. PDGFRA mutations are found in most of the GISTs that do not have the KIT mutation. KIT and PDGFRA mutations are never present together.
- SDH and BRAF genes: A minuscule proportion of GISTs that do not have either KIT or PDGFRA mutations, may have SDH or BRAF gene mutations.
Current knowledge does not indicate any life-style related or environmental risks for GIST, and consequently, there are no known ways to prevent GIST. Known risk factors for developing GIST are very few, which include advanced age and certain inherited syndromes, though GISTs are rarely hereditary.
The hereditary syndromes that have a higher risk for GIST include:
- Primary familial GIST syndrome: An inherited mutation in KIT or PDGFRA genes that increases the risk for developing GIST. People with this syndrome may also develop other conditions such as:
- Carney triad: Coexistence of three types of tumors, GIST, benign tumors in the lungs known as pulmonary chondroma, and nerve tumors are known as paraganglioma, primarily in young women.
- Neurofibromatosis type 1 (von Recklinghausen disease): Inherited or sporadic mutation in the NF1 gene, which can cause GISTs and growths under the skin.
- Carney-Stratakis syndrome: An inherited condition caused by SDH gene mutation with higher risk for GIST and paraganglioma.
What is the treatment for GIST tumor?
Treatment for GISTs depends on factors such as:
- Tumor size
- Tumor location
- Tumor stage, whether it is benign or has spread to other parts
- How fast the tumor is growing (mitotic rate)
- Chances of tumor recurrence
Traditional cancer treatment with chemotherapy has not been found to be effective for GISTs and seldom used. Radiation may be used as palliative treatment to relieve pain or arrest bleeding. It is also possible to enroll in clinical trials for new treatments. Currently, the types of treatment for GISTs include the following:
Surgery is usually the primary treatment for GISTs. Tumors smaller than 2 cm may just be watched with periodic endoscopy. Localized tumors larger than 2 cm are usually surgically removed either with open surgery or a minimally invasive laparoscopic surgery.
Ablation is the use of extreme heat or cold to destroy the tumor. Ablation also destroys some normal tissue around the tumor and may not be suitable for tumors in some locations. Ablation may be used when GIST has spread to the liver and if surgery is not possible. Types of ablation include:
- Radiofrequency ablation: Use of radio waves to break up the tumor
- Ethanol ablation: Injection of ethanol into the tumor
- Microwave thermotherapy: Use of heat from the microwave
- Cryotherapy: Freezing off the tumor using a thin metal probe
Embolization is a procedure that selectively blocks the blood supply to the tumor and is used mostly for GIST that has spread to the liver. There are three types of embolization:
- Trans-arterial embolization (TAE): A thin tube is advanced through the hepatic artery to deliver particles that plug the artery providing blood supply to the tumor.
- Radioembolization: Injection of radioactive particles at the tumor site to block its blood supply.
- Chemoembolization: Injecting chemotherapy medication into the tumor before blocking its blood supply.
Targeted therapy medications used for GIST are known as tyrosine kinase inhibitors, which specifically block the activity of a group of proteins known as tyrosine kinases. Targeted therapy is an effective treatment for GIST because, KIT and PDGFRA, which cause most GISTs, are tyrosine kinase proteins.
Targeted therapy may be used to prevent recurrence of the tumor, to shrink the tumor before surgery, or to treat advanced an tumor that has spread. FDA-approved targeted therapy medications for the treatment of GIST are:
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Is GIST cancer curable?
Localized GISTs which are caught early can be successfully treated with surgery. Tumors that are smaller than 5 cm have good chances for remission. Tumor location also influences the outcome; for instance, a tumor in the stomach is less aggressive than a tumor of the same size and mitotic rate in the small intestine.
Targeted therapy with imatinib has been highly effective for GIST because it targets both KIT and PDGFRA gene mutations which are responsible for more than 95% percent of GISTs. More therapies are under research, which is further likely to improve the efficacy of GIST treatment.
What is the survival rate for GIST cancer?
The survival rate for GIST varies with the size and location of the tumor and its mitotic rate. Some GISTs are slow-growing while others grow aggressively and spread to the liver or keep recurring.
The 5-year survival rate for a localized GIST is 93%. The five-year survival rate drops to 80% if GIST has spread to nearby areas or organs. GISTs that have metastasized to distant parts at the time of diagnosis have a 5-year survival rate of 55%.
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