Gastrointestinal stromal tumours (GISTs)

Gastrointestinal stromal tumours (GISTs) start in special cells of the gastrointestinal (GI) tract called interstitial cells of Cajal. They have characteristics of both smooth muscle cells and nerve cells. They receive messages (signals) from the nervous system to make muscles of the GI tract tighten (contract) and relax (expand). The tightening and relaxing of these muscles (called peristalsis) moves food and liquid through the digestive system.

GISTs can happen anywhere in the GI tract, but they develop most often in the stomach. The small intestine is the second most common location. GISTs can also develop in the esophagus, colon and rectum.

Most GISTs have a change (mutation) in the KIT (c-KIT) gene that causes the body to make too much of the KIT protein. The second most common change in GISTs is in the PDGFR-alpha gene (platelet-derived growth factor receptor-alpha gene). This change causes the body to make too much PDGFR-alpha protein. Both the KIT and PDGFR-alpha proteins are enzymes called tyrosine kinases, which help cells grow, divide and move around.

GISTs can be non-cancerous (benign) or cancerous (malignant).

Non-cancerous GISTs do not spread (metastasize) to other parts of the body. They are not usually life-threatening. GISTs that are smaller than 2 cm are usually non-cancerous.

GISTs can also be cancerous (malignant). A cancerous GIST can grow into nearby tissue and destroy it. It can also spread to other parts of the body.

GISTs can develop at any age, but they usually happen in people over 50.

Almost all GISTs happen sporadically. This means there is no clear reason why they develop. In a small number of people, GISTs develop due to an inherited condition, including:

• familial GIST syndrome – having many GISTs
• neurofibromatosis type 1
• Carney-Stratakis syndrome – having both GISTs and paragangliomas

A GIST may not cause any signs or symptoms in its early stages. Signs and symptoms often appear as the tumour grows and causes problems such as pain and bleeding.

The signs or symptoms of GISTs include:

• blood in the stool or vomiting blood
• fatigue caused by a low number of red blood cells (anemia)
• pain or discomfort in the abdomen
• nausea and vomiting
• feeling full
• weight loss
• a lump in the abdomen
• problems swallowing

Diagnosing a GIST may begin with a visit to your family doctor. Your doctor will ask you about any symptoms you have and may do a physical exam. Sometimes a GIST is found by chance when you have tests for other reasons. Your doctor may refer you to a specialist or order certain tests to check for a GIST or other health problems.

The following tests may be used to rule out or diagnose a GIST:

• blood tests, such as a complete blood count (CBC) and blood chemistry tests
• imaging tests, such as a CT scan, an MRI or a PET scan
• endoscopy (sometimes with an ultrasound), such as a gastroscopy or a colonoscopy
• biopsy, which is often done during an endoscopy

GISTs are described or classified based on how much cancer there is in the body and where it is when first diagnosed. This is often called the extent of cancer. Information from tests is used to find out:

• where the GIST started
• the size of the tumour
• how quickly the cancer cells grow and divide (called the mitotic rate)
• whether the cancer has spread from where it first started
• where the cancer has spread

Your healthcare team uses this information to plan treatment and estimate the outcome (your prognosis).

When describing the extent of a GIST, doctors may use the words localized or metastatic. Localized means that the cancer is only in the organ where it started or close to it and has not spread to other parts of the body. Metastatic means in a part of the body farther from where the GIST started, such as the liver or peritoneal cavity.

A recurrent GIST is cancer that has come back (recurred) after it has been treated. If it comes back in the same place or close to where the cancer first started, it’s called local recurrence. It can also recur in another part of the body. This is called metastatic GIST.

Cancer cells can spread from where the GIST started to other parts of the body. This spread is called metastasis.

Understanding how a type of cancer usually grows and spreads helps your healthcare team plan your treatment and future care. If a GIST spreads, it can spread within the abdomen to the liver or peritoneal cavity. It can also spread to the lungs or bones, but this is not common.

Knowing how quickly the cancer is growing and how likely it is to spread helps doctors plan your treatment. It can also help the healthcare team predict future outcomes (your prognosis) and how the cancer might respond to treatment.

A pathologist examines a tissue sample from the tumour under a microscope to see how often the cells are dividing. They also check the size of the tumour and where the tumour is in the body. Then GISTs are classified as low or high risk based on their chance of progressing. Low-risk GISTs, which grow slowly, are small and are in the stomach, tend to have a better prognosis.

GISTs are different than other types of soft tissue sarcoma, so they are treated differently. When deciding which treatments to offer for a GIST, your healthcare team will consider:

• where the GIST is in the body
• if it’s a low-risk or high-risk GIST
• if surgery can be done (it’s resectable) or not (it’s unresectable)
• types of gene mutations in the GIST
• your overall health
• what you prefer or want

You may be offered one or more of the following treatments for a GIST.

Surgery is the main treatment for GISTs that haven’t spread (metastasized). The cancer is removed along with some normal tissue around it (called a complete resection). Depending on the size of the tumour and where it is in the GI tract, you may have one of the following surgeries:

Wedge or segmental resection removes a section of the stomach containing a small GIST.

Gastrectomy removes part or all of the stomach through a cut (incision) in the abdomen. It is done for GISTs in the stomach. Find out more about surgery for stomach cancer, including a gastrectomy.

Bowel resection removes part of the small intestine or large intestine or both. Find out more about a bowel resection.

En bloc resection removes the tumour and surrounding areas as one piece. It is used for GISTs that are attached to nearby organs.

Sometimes surgery may be done using a laparoscopic technique. With the laparoscopic technique, the surgeon makes small cuts in the abdomen and then inserts an endoscope (a thin, tube-like instrument with a light and lens) with tools to do the surgery. If laparoscopic surgery can’t be done, an open technique is used to make a large cut in the abdomen to reach the intestine.

Targeted therapy uses drugs to target specific molecules (such as proteins) on or inside cancer cells to stop the growth and spread of cancer and limit harm to normal cells. The targeted therapy drugs used for GISTs are called tyrosine kinase inhibitors. These drugs block many different proteins, including the KIT protein, to help stop or slow cancer cells from growing and spreading. They also prevent tumours from developing new blood vessels.

The following drugs are taken daily as a pill. For many cases, they are given until the disease gets worse or you can’t cope with the side effects of the treatment.

Imatinib (Gleevec) may be used after removing a GIST with a KIT gene mutation and when there is a high risk that the GIST will come back. It may also be used for unresectable or metastatic GISTs.

Sunitinib (Sutent) may be given for unresectable or metastatic GISTs if imatinib doesn’t work.

Regorafenib (Stivarga) may be used for unresectable or metastatic GISTs that have progressed after treatment with imatinib and sunitinib.

For more detailed information on specific drugs, go to sources of drug information.