A gastrointestinal stromal tumor (GIST) is a type of cancer that begins in the digestive system. GISTs happen most often in the stomach and small intestine.

A GIST is a growth of cells that's thought to form from a special type of nerve cells. These special nerve cells are in the walls of the digestive organs. They play a part in the process that moves food through the body.

Small GISTs may cause no symptoms, and they may grow so slowly that they don't cause problems at first. As a GIST grows, it can cause signs and symptoms. They might include:

• Abdominal pain
• A growth you can feel in your abdomen
• Fatigue
• Nausea
• Vomiting
• Cramping pain in the abdomen after eating
• Not feeling hungry when you would expect to
• Feeling full if you eat only a small amount of food
• Dark-colored stools caused by bleeding in the digestive system

GISTs can happen in people at any age, but they are most common in adults and very rare in children. The cause of most GISTs isn't known. A small number are caused by genes passed from parents to children.

To diagnose a GIST, your health care provider might start by asking you about your symptoms and your health. Your provider may also check for a growth in your abdomen.

If symptoms suggest that you may have a GIST, you might need other tests to find the tumor. These tests may include:

• Imaging tests. Imaging tests help your health care team find your tumor and see its size. Tests might include ultrasound, CT, MRI and positron emission tomography (PET) scans. Not everyone needs every test.
• Upper endoscopy. This test uses a long, thin tube (endoscope) with a light on the end. The tube goes through the mouth and down the throat. This test looks at the inside of the esophagus, stomach and the first part of the small intestine.
• Endoscopic ultrasound (EUS). This test also uses an endoscope, but with an ultrasound probe on the tip of the scope. The ultrasound probe uses sound waves to make pictures of the tumor and show its size.

• Fine-needle aspiration biopsy. This test collects a small sample of tissue from the tumor so it can be tested in a lab. This test is like EUS, but with a thin, hollow needle on the tip of the endoscope. The EUS finds the tumor. The needle collects small amounts of tissue for the lab tests.

  Sometimes the needle can't get enough cells, or the results aren't clear. You might need surgery to collect the sample.

• Laboratory tests on biopsies. The biopsy sample from your tumor goes to a lab for testing. In the lab, specialists test the cells to see if they're cancer cells. Other tests give your provider details about your cancer cells that are used to plan your treatment.

GIST treatment often involves surgery and targeted therapy. Which treatments are best for you depends on your situation.

Some GISTs don't need treatment right away. Very small GISTs that don't cause symptoms might not need treatment. Instead, you might have tests to see if the cancer grows. If your GIST grows, you can start treatment.

Surgery

The goal of surgery is to remove all the GIST. It's often the first treatment for GISTs that haven't spread to other parts of the body.

Surgery might not be used if your tumor grows very large or if it grows into nearby structures. If this happens, your first treatment might be targeted drug therapy to shrink the tumor. You might have surgery later.

The type of operation you have depends on your cancer. Often surgeons can access the GIST using minimally invasive surgery. This means surgical tools go through small cuts in the abdomen rather than through one large cut.

Targeted drug therapy

Targeted drug treatments focus on specific chemicals present within cancer cells. By blocking these chemicals, targeted drug treatments can cause cancer cells to die. For GISTs, the target of these drugs is an enzyme called tyrosine kinase that helps cancer cells grow.

Targeted drug therapy for GISTs often begins with imatinib (Gleevec). Targeted drug treatments can be given:

• After surgery to lower the risk that the cancer will come back
• Before surgery to shrink the tumor and make it easier to remove
• As the first treatment if the cancer has spread to other parts of the body
• If the GIST comes back

Other targeted drugs might be used if imatinib doesn't work for you or if it stops working. Targeted drug therapy is an active area of cancer research, and new drugs are likely to become options in the future.