Cancer begins when the cells of the body are getting out of control. Cells in almost any part of the body can become cancerous and can spread to other parts of the body.
Gastrointestinal stromal tumors (GISTs) start in special cells in the wall of the gastrointestinal tract (GI), also known as the digestive tract.

These tumors begin from early forms of special cells in the wall of the GI pathway, called intermediate Cajal cells (ICCs). ICCs are cells of the autonomic nervous system, the part of the nervous system that regulates the body’s processes, such as digesting food. ICCs are sometimes called “GI’s” pacemakers because they send the muscles of the organs a signal to contract in order to transport and promote food and fluids.

More than half of GISTs develop in the stomach, while the rest develop in the small intestine, or anywhere along GI Street. A small number of GISTs develop outside the gastrointestinal tract in nearby areas, such as the omentum (a layer of adipose tissue above the organs in the abdomen) or the peritoneum (a tissue layer like a membrane that surrounds the organs and the inner abdominal wall).

Different cancers have different risk factors. Some risk factors, such as smoking, may change. Others, such as a person’s age or family history, cannot be changed.
But having one risk factor, or even many does not mean that one person will get the disease. Like many people having the disease, they may have few or no known risk factors.
Currently, there are very few known risk factors for gastrointestinal stromal tumors (GISTs).
Age
These tumors may occur in people of any age, but are rare in people under the age of 40 and are more common in people aged 50 to 80 years old.

Genetic syndromes
Most GISTs are sporadic (not inherited) and have no clear cause. In rare cases, however, GISTs were found in several members of the same family. These family members have inherited a genetic mutation (change) that can lead to GISTs.

Primary GIST family syndrome: This is a rare, inherited condition that leads to an increased risk of developing GISTs. People with this condition tend to develop GISTs at a younger age and are more likely to have more than one GIST. This syndrome is caused by an abnormal KIT gene that is passed from the parent to the child. This is the same gene that mutates (changes) in most sporadic forms of GISTs. People who inherited this mutated gene from one parent have it in all their cells, while people with sporadic GISTs only have it in cancer cells.
Also, a mutation in the PDGFRA gene causes this genetic syndrome. Mutations in the PDGFRA gene are present in approximately 5% to 10% of sporadic GISTs.

Type 1 neurofibromatosis (von Recklinghausen‘s disease): This disease is caused by a mutation in the NF1 gene. This gene mutation can be inherited from a parent, but in some cases, it occurs before birth without being inherited.

People with this syndrome often have many benign (non-cancerous) tumors that form in the nerves, called neurinomas, starting at an early age. These tumors form under the skin, usually giving a brown patch on the skin (called café au lait spots). People with this condition are at higher risk for GIST, as well as some other types of cancer

Carney-Stratakis Syndrome: People with this rare inherited condition have an increased risk of developing GISTs (more often in the stomach), as well as nerve tumors called paragangliomas, which are more common in adolescents. They are also more likely to have more than one GIST. This syndrome is caused by a mutation in one of the genes of succinic dehydrogenase (SDH), which passes from parent to child.

Up until now, no effective screening tests have been found for gastrointestinal stromal tumors (GISTs), so regular testing of asymptomatic people is not recommended.
Many GISTs are detected due to the symptoms a person has, but some GISTs can be found early by chance.

They sometimes appear on an examination for another problem, such as during a colonoscopy, to investigate the possibility of colon cancer. Rarely, a GIST tumor may be seen on an imaging test, such as computed tomography (CT scan). Some GISTs may also be found accidentally (unexpectedly) during abdominal surgery for another problem.

Once someone is diagnosed with cancer, doctors will try to figure out if it has spread, and if so, to what extent. This process is called staging. It helps to determine how serious the cancer is and how it can be treated better. Doctors also use cancer staging for survival statistics.

Stages for gastrointestinal stromal tumors (GIST) range from stages I (1) to IV (4). As a rule, the smaller the number, the less cancer has spread. A higher number, such as stage IV, means that cancer has spread more. Although everyone’s cancer experience is unique, cancers with similar stages tend to have a similar perspective and are often treated in the same way.

 How is the stage determined?
It is used by the American Joint Committee on Cancer (AJCC) TNM, which is based on 4 basic pieces of information:
• The extent of the tumor (T): How big is cancer?
• Proliferation in nearby lymph nodes (N): Has cancer spread to nearby lymph nodes?
• Metastasis to distant areas (M): Has cancer spread to distant organs such as the liver?
• The mitotic activity index is a measure of laboratory testing on how quickly may cancer cells grow and divide. It is described as low or high. A low mitotic index predicts a better outlook.

The staging system uses the pathological stage (also called the surgical stage). It is determined by histological examination of the tissue that is removed during operation (surgery).

Sometimes, if surgery is not possible, cancer will get a clinical stage. This is based on the results of the physical examination, the histological examination of the biopsy, and imaging tests. The clinical-stage will be used to help and schedule a treatment. Sometimes, though, cancer has spread beyond the estimates of the clinical stage and may not predict the patient’s prospects as accurately as with a histopathological staging.

Cancer staging can be complex, so ask your doctor to explain it to you in a way you understand.

Survival rates can give you an idea of ​​what percentage of people with the same type and stage of cancer are still alive for some time (usually 5 years) after diagnosis. They may not tell you how long you will live, but they can help you better understand how successful your treatment is.

Keep in mind that survival rates are estimates and are often based on previous results from a large number of people who have had a particular cancer, but cannot predict what will happen in the event of a particular person. These statistics can be confusing and can lead to more questions. Discuss with your doctor about how these numbers may apply to you, as he or she is familiar with your condition.

What is the 5-year relative survival rate?
A relative survival rate compares individuals with the same type and stage of the gastrointestinal stromal tumors (GIST) in individuals with the total population. For example, if the relative 5-year survival rate for a particular GIST stage is 90%, it means that people with this type of cancer are on average about 90% more likely to be alive, 5 years after diagnosis in comparison with people who don’t have cancer.

Where do these numbers come from?
The American Cancer Society is based on information from the SEER * database maintained by the National Cancer Institute (NCI) to provide survival statistics for various types of cancer.

The SEER database monitors the relative 5-year survival rates for GIST in the United States, based on the extent of the spread of cancer. The SEER database, however, does not group cancers from the stages of AJCC TNM (stage 1, stage 2, stage 3, etc.). Instead, it groups cancers in local, regional, and distant stages:

 Local (localized): The cancer is confined to the organ where it started.
Peripheral (regional): Cancer has developed in nearby tissues or has spread to nearby lymph nodes.
Distant: Cancers have spread to distant parts of the body, such as the liver.

Relative 5-year survival rates for GIST
(Based on individuals diagnosed with GIST between 2008 and 2014.)

* SEER = Surveillance, Epidemiology, and End Results

Understanding the Numbers
These numbers only apply to the cancer stage at first diagnosis. They do not apply later if cancer grows, spreads, or recurs after treatment.

Survival rates are grouped based on the extent of cancer, but also your age, overall health, cancer resection, the degree to which cancer responds to treatment, and other factors that may also affect your survival prospects.

People now diagnosed with GIST may have better prospects than these numbers. The treatments are improving over time and these numbers are based on people diagnosed and treated at least five years earlier.