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  4. Gastrointestinal Stromal Tumors (GIST): Staging and Treatment
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Gastrointestinal Stromal Tumors (GIST): Staging and Treatment

Author: Marisa Healy, BSN, RN
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Last Reviewed: May 17, 2024

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What is staging for cancer?

Staging is the process of learning how much cancer is in your body and where it is. Tests like biopsies (endoscopic ultrasound fine-needle aspiration), CTs, and PET scans are done to help stage your cancer. A biopsy is needed to diagnose a gastrointestinal stromal tumor (GIST). These tumors are soft and fragile. Care needs to be taken while doing the biopsy to lower the risk of bleeding, tumor rupture, and intra-abdominal (inside the belly) tumor spread. Your providers need to know about your cancer and your health so that they can plan the best treatment for you.

Staging looks at the size of the tumor and where it is, and if it has spread to other organs. The staging system for GIST is called the “TNM system,” as described by the American Joint Committee on Cancer. It has three parts:

  • T: describes the size/location/extent of the "primary" tumor.
  • N: describes if the cancer has spread to the lymph nodes.
  • M: describes if the cancer has spread to other organs (metastases).

Your healthcare provider will use the results of the tests you had to figure out your TNM result and combine these to get a stage from I to IV.

How is GIST staged?

GIST is staged using the TNM system, with the addition of the “G” or histologic grade of the tumor. The G describes  the mitotic rate, or how fast the cancer cells are growing and dividing.

Staging is based on:

  • The size of your tumor.
  • If there is spread to the lymph nodes or other organs (metastasis).
  • Biopsy results.
  • Mitotic rate.

There are two different staging groups, depending on where the cancer started: 

  • The first group includes the stomach or omentum.
  • The second group includes the small intestine, esophagus, colon, rectum, or peritoneum. 

Staging is important because it helps guide your treatment options. The staging systems are complex, and some stages have more than one TNM stage. Below is a summary of the staging systems. Talk to your provider about the stage of your cancer.

GIST (Stomach or omentum)

  • IA (T1 or T2, N0, M0, low mitotic rate): The tumor is 2 centimeters (cm) or less, or larger than 2cm but not more than 5cm AND it has not spread to lymph nodes or other parts of the body.
  • IB (T3, N0, M0, low mitotic rate): The tumor is bigger than 5cm but not bigger than 10cm, and has not spread to lymph nodes or other parts of the body.
  • II (T1, N0, M0, high mitotic rate): The tumor is not more than 2cm and has not spread to lymph nodes or other parts of the body.
  • II (T2, N0, M0, low mitotic rate): The tumor is larger than 2cm but no more than 5cm and has not spread to lymph nodes or other parts of the body.
  • II (T4, N0, M0, low mitotic rate): The tumor is bigger than 10cm but has not spread to lymph nodes or other parts of the body.
  • IIIA (T3, N0, M0, high mitotic rate): The tumor is bigger than 5cm but not bigger than 10cm and has not spread to lymph nodes or other parts of the body.
  • IIIB (T4, N0, M0, high mitotic rate): Tumor is larger than 10cm and has not spread to nearby lymph nodes or other parts of the body.
  • IV (Any T, N1, M0, high or low mitotic rate): The tumor is any size and has spread to the lymph nodes but not to other parts of the body.
  • IV (Any T, Any N, M1, high or low mitotic rate): The tumor is any size, and may have spread to lymph nodes, and has spread to other parts of the body.

GIST (Small intestine, esophagus, colon, rectum, or peritoneum)

  • I (T1 or T2, N0, M0, low mitotic rate): The tumor is smaller than 2cm or larger than 2cm, but less than 5cm across AND has not spread to lymph nodes or other parts of the body.
  • II (T3, N0, M0, low mitotic rate): The tumor is 5cm or bigger but not more than 10cm, and has not spread to lymph nodes or other parts of the body.
  • IIIA (T1, N0, M0, high mitotic rate): The tumor is no more than 2cm and has not spread to lymph nodes or other parts of the body.
  • IIIA (T4, N0, M0, low mitotic rate): The tumor is bigger than 10cm and has not spread to nearby lymph nodes or to distant sites.
  • IIIB (T2, N0, M0, high mitotic rate): The tumor is larger than 2cm but not more than 5cm and has not spread to lymph nodes or distant sites.
  • IIIB (T3, N0, M0, high mitotic rate): The tumor is larger than 5cm but not more than 10cm and has not spread to lymph nodes or other parts of the body.
  • IIIB (T4, N0, M0, high mitotic rate): The tumor is larger than 10cm but has not spread to lymph nodes or other parts of the body.
  • IV (Any T, N1, M0, high or low mitotic rate): The tumor is any size, and has spread to the lymph nodes but not to other parts of the body.
  • IV (Any T, Any N, M1, high or low mitotic rate): The tumor is any size, may or may not be in the lymph nodes, and has spread to other parts of the body.

The stage of your cancer will help your care team choose the best treatment for you.

How is GIST treated?

Treatment for GIST depends on many factors, like your cancer stage, overall health, and the results of your tests. Your treatment may include:

Surgery

Surgery can be used to treat most cases of GIST. GIST are unlike other tumors because they are very soft and fragile. A surgeon must be very careful to not break or rupture the tumor. You need a surgeon familiar with GIST to do your surgery. The type of surgery you have will depend on the size of your tumor and where it is.

If your tumor has spread to other organs, those tumors and parts of organs may also need to be removed. In some cases, imatinib, a targeted therapy, may be given for a few months to shrink the tumor. This can make it easier to remove during surgery.

Targeted Therapy

GIST cells tend to have genetic mutations found during a biopsy. Targeted therapies target certain genetic mutations and can be used to treat GIST. Tyrosine kinase inhibitors are often used. They block the action of a specific enzyme called tyrosine kinase. By blocking these enzymes, the tumor can stop growing and shrink. The primary targeted therapy used in the treatment of GIST is imatinib. Imatinib targets KIT and PDGFRA proteins. This medication can be used before surgery or after surgery, usually for 1-3 years depending on tumor size and location. The goal of taking this medication after surgery is to keep the tumor from coming back. This may be called maintenance therapy. Other targeted therapies used are:

  • Sunitib: This medication targets KIT and PDGFRA along with other proteins and can be used if imatinib stops working.
  • Regorafenib: Also targets many proteins including KIT and PDGFRA. It is used when imatinib and sunitinib stop working or if a patient cannot take them.
  • Ripretinib: Also targets many proteins including KIT and PDGFRA. It is used when imatinib, sunitinib, or regorafenib stop working or if a patient cannot take them.
  • Avapritinib: This therapy targets PDGFRA, KIT, and other proteins. It is used to treat advanced cases with a change in the PDGFRA gene called an exon 18 mutation.

Sorafenib, nilotinib, dasatinib, and pazopanib may be used if the previous medications are no longer working.

Interventional Procedures

Procedures called ablation and embolization may be used if the GIST has spread to the liver. Ablation destroys tumor tissue using heat, cold, or chemicals. There are a few types that can be used:

  • Radiofrequency Ablation: High-energy radio waves are used to kill cancer cells.
  • Ethanol Ablation: Alcohol is injected into the tumor to kill cancer cells.
  • Microwave Thermotherapy: Microwaves go into the tumor through a probe. The heat kills cancer cells.
  • Cryosurgery: The tumor cells are frozen using a thin metal probe.

Embolization is when somethng is injected into a tumor to stop or lessen blood flow to the cancer cells in the liver. The most common type of embolization used to treat the liver in GIST is trans-arterial embolization. A thin, moveable tube is put into an artery and threaded up into the liver. Once placement is confirmed, the substance is injected into the artery to stop blood flow.

These procedures can cause side effects and you may need to spend time in the hospital. Talk to your provider about which procedure is best for you.

Radiation Therapy

Radiation is the use of high-energy x-rays to kill cancer cells. Radiation therapy is not often used in the treatment of GIST. However, it may be used to manage symptoms, such as pain from metastatic cancer.

Clinical Trials

You may be offered a clinical trial as part of your treatment plan. To find out more about current clinical trials, visit the OncoLink Clinical Trials Matching Services.

Making Treatment Decisions

Your care team will make sure you are included in choosing your treatment plan. This can be overwhelming as you may be given a few options to choose from. It feels like an emergency, but you can take a few weeks to meet with different providers and think about your options and what is best for you. This is a personal decision. Friends and family can help you talk through the options and the pros and cons of each, but they cannot make the decision for you. You need to be comfortable with your decision – this will help you move on to the next steps. If you ever have any questions or concerns, be sure to call your team.

ACS Gastrointestinal Stromal Tumors http://www.cancer.org/cancer/gastrointestinalstromaltumorgist/index

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