Gastrointestinal stromal tumor

A gastrointestinal stromal tumor (GIST) is a type of cancer that develops in the gastrointestinal (GI) tract. GISTs belong to a different family of cancers called soft tissue sarcomas. These tumors start in the tissues that connect and support the body. That's why they are unlike other cancers found in the GI tract, such as stomach or colon adenocarcinoma.

GISTs are a rare type of cancer that may develop anywhere in the GI tract, though they most commonly are detected in the stomach or small intestine. The most important thing to know about a GIST is how fast it grows. Some grow quickly and spread—these need to be treated. Others grow slowly and never spread—these may never even cause symptoms. They may be watched (through surveillance methods) instead of treated immediately.

What causes a GIST?

A risk factor is anything that increases the risk of cancer developing. Unlike other cancers that have lifestyle risk factors such as smoking or certain diets, GISTs don’t appear to have known risk factors. This makes it difficult to recommend behaviors to modify to reduce the risk.

A GIST is caused by abnormal cells that start to grow out of control. Although researchers don’t know what exactly causes a GIST, developing one is more likely if you inherit an abnormal gene, called a mutation, from a biological parent. In rare cases, GISTs may occur in several members of the same family.

Genes aren’t the only risk factor. In fact, most GISTs occur after birth and aren’t inherited. You may be at higher risk if you’re older than 50, and GISTs are slightly more common in men than in women.

What are the symptoms of a GIST?

Many people with a GIST don’t show symptoms if the tumor is small and not growing. If symptoms develop, they may be caused by bleeding and include vomiting blood or having blood in the stool (bright red or very dark). Bleeding caused by a GIST may also lead to anemia (low blood count), which may lead to tiredness and fatigue.

GIST patients may also experience:

• Belly pain
• Pain or difficulty when swallowing
• Loss of appetite
• Feeling of fullness soon after eating
• Weight loss

How is a GIST diagnosed?

A GIST may be found incidentally during a test for another condition. Regardless of whether the patient has symptoms, or the GIST was discovered during other procedures, doctors typically recommend diagnostic tests to learn the tumor's grade in order to recommend treatment. It’s important to know whether it’s the type that grows slowly or quickly. Common tests used to diagnose a GIST, or learn more about the characteristics of one, include:

• Computed tomography (CT) scan
• Magnetic resonance imaging (MRI)
• Endoscopy and endoscopic ultrasound (with biopsy)
• CT/PET (positron emission tomography) scan

A biopsy is often performed, taking a sample of tissue from the tumor to be studied by a pathologist. The tumor cells are studied for substances and genetic mutations to help doctors learn more about how to best treat it. Doctors may test for tumor markers (proteins) that may be used as targets during treatment, called targeted therapy. They may also get the grade and mitotic count, which tells how fast the cancer cells are replicating and growing.

How is a GIST staged?

After all the diagnostic tests have been reviewed, doctors may stage the cancer, which helps guide treatment. Unlike other types of GI cancers, a GIST isn’t staged in stages 1 through 4. Instead, GISTS are staged into groups based on the tumor size and mitotic rate, which helps to predict the likelihood of metastases (or spread to other organs).

The two main classifications for GISTs are:

• Resectable, which means the cancer may be completely removed with surgery
• Unresectable, which means the cancer is unable to be completely removed surgically due to the tumor's involvement with other organs or blood vessels, or due to spread to distant organs

Other characteristics of a GIST that guide treatment plans include whether it’s:

• Metastatic, meaning it has spread to another part of the body
• Recurrent, meaning the tumor has returned after treatment
• Refractory, meaning the tumor hasn’t responded to treatment

How is a GIST treated?

A treatment plan depends on the characteristics of the cancer, as well as the patient’s age, personal preference and overall physical health. The basic treatment options for a GIST include:

• "Watchful waiting" or surveillance—A small GIST with low mitotic rate that’s growing slowly and not causing symptoms may be treated with watchful waiting. Doctors will likely conduct periodic checkups and wait to see whether the tumor starts to grow enough to cause symptoms.
• Surgery—A resectable GIST may be completely removed with surgery. Surgery is the most common GIST treatment.
• Targeted therapy—These drugs are the main treatment for an unresectable, recurrent or metastatic GIST. In some cases, targeted therapy may also be used to shrink a tumor before surgery or to treat the remaining tumor after surgery, or it may be given for several years to prevent a GIST from returning. These drugs, called tyrosine kinase inhibitors (TKIs), are taken as pills at home, and they block the signals (kinases) that tell tumors to grow. Side effects depend on the type of TKI—since there are several types approved to treat GISTs—but may include diarrhea, nausea, rash or fatigue.

Unlike other GI cancers, chemotherapy and radiation therapy aren’t usually recommended for treating GISTs. Targeted treatment and other new treatments are typically done as part of a clinical trial. Patients should ask whether clinical trials are the right approach for them.

What is the prognosis for a GIST?

A GIST is rare—it makes up less than 1 percent of GI tumors, according to the American Society of Clinical Oncology (ASCO).

Because everyone’s response to cancer treatment is different, doctors calculate the percentage of people alive with cancer at five years from diagnosis. This is called the five-year survival rate—and it gives them an idea of the overall prognosis, or chance of recovery, for that type of cancer.

Looking at all types of GISTs together, the five-year survival rate is 83 percent, according to ASCO. For GISTs that haven’t spread away from the GI tract where they started, the five-year survival rate is high—as high as 93 percent. For GISTs with distant spread, the five-year survival rate drops to 55 percent. Specific survival rates for this disease depend on several factors, including tumor size, mitosis rate, location and treatment.

It’s important to remember that the five-year survival rate may change in the next five years as new treatments become available through clinical trials.