Gastrointestinal stromal tumours (GISTs)

Gastrointestinal stromal tumours (GISTs) are a rare type of soft tissue sarcoma. They start in specialized cells (called interstitial cells of Cajal) that are found in the walls of the gastrointestinal (GI) tract. These cells help the GI tract tighten (contract) and relax (expand). The tightening and relaxing of these muscles (called peristalsis) is the process that 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 be non-cancerous (benign) or cancerous (malignant).

Most GISTs have a change (a mutation) in one of the genes that help cells grow, divide and move around (either the KIT gene or the PDGFR-alpha gene).

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 most common signs and symptoms of GISTs are blood in the stool, vomiting blood, fatigue, pain or a lump in the abdomen, or always feeling full.

Grading describes how the cancer cells look compared to normal, healthy cells. GISTs are graded based on the mitotic rate. The mitotic rate measures how fast cancer cells are dividing and growing. It is the number of cells that divide (mitosis) in a certain amount or area of cancer tissue.

GISTs can have a low or high mitotic rate.

Staging describes or classifies a cancer 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.

Staging GISTs depends on the mitotic rate (grade) and where the cancer starts. Talk to your healthcare team about staging for GISTs.

Your healthcare team will suggest treatments based on your needs and work with you to develop a treatment plan.

When deciding which treatments to offer for a GIST, your healthcare team will consider:

• where the GIST is in your body
• if it has a low or high mitotic rate
• if the GIST can be removed (resectable)
• whether it has the KIT gene or PDGFR-alpha gene mutation
• your overall health
• what you prefer or want

You may be offered the following treatments for a GIST.

Surgery is the main treatment for GISTs that haven’t spread (metastasized). The main goal of surgery is to remove the whole tumour along with some normal tissue around it (called the surgical margin). The other tissues, structures and organs that need to be removed will depend on where the cancer is.

For GISTs that begin in the stomach, you may have part or all of the stomach removed (called a gastrectomy) .

For GISTs that begin in the intestines, you may have part of the small intestine or large intestine removed (called a bowel resection) .

Targeted therapy uses drugs to target specific molecules (such as proteins) on cancer cells or inside them. These molecules help send signals that tell cells to grow or divide. By targeting these molecules, the drugs stop the growth and spread of cancer cells, and limit harm to normal cells.

The targeted therapy drugs used for GISTs are called tyrosine kinase inhibitors. Tyrosine kinase inhibitors (TKIs) block chemicals called tyrosine kinases. These chemicals are part of the signalling process within cells. When this process is blocked, the cancer cells stop growing and dividing.

Imatinib (Gleevec) may be given after surgery for a GIST with a KIT gene mutation if there is a high risk that the GIST will recur (come back). It may also be used for advanced or metastatic GISTs if surgery can’t be done (unresectable).

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

Regorafenib (Stivarga) may be given for unresectable or metastatic GISTs if imatinib and sunitinib donʼt work.

Imatinib, sunitinib and regorafenib are taken daily as a pill by mouth (orally).