Stages and Other Prognostic Factors of Gastrointestinal Stromal Tumors

If you are diagnosed with a gastrointestinal stromal tumor (GIST), your cancer care team will try to figure out if it has spread, and if so, how far. This process is called staging.

The stage of a cancer describes how much cancer is in the body. It helps determine how serious the cancer is and how best to treat it.

How are gastrointestinal stromal tumors staged?

The AJCC staging system gives a detailed summary of how far a GIST has spread. But for treatment purposes, doctors are often more concerned about whether the tumor can be resected (removed) completely with surgery.

Resectable or unresectable

Whether a tumor is resectable depends on its size, location, if it has spread to other parts of the body, and if a person is healthy enough for surgery:

• Tumors that can clearly be removed without causing major health problems are defined as resectable.
• Tumors that can’t be removed completely, because they have spread or for other reasons, are described as unresectable.
• In some cases, doctors might describe a tumor as marginally resectable or borderline resectable if it’s not clear if it can be removed completely.

If a tumor is considered unresectable or marginally resectable when it is first found, targeted therapy might be used first to try to shrink the tumor enough to make it resectable.

The AJCC TNM staging system

The staging system most often used for GIST tumors is the American Joint Committee on Cancer (AJCC) TNM system.

This staging system is based on 4 key pieces of information:

• Size of the primary tumor (T) describes the size of the main tumor.
• Spread to lymph nodes (N) describes the extent of spread to nearby (regional) lymph nodes. GISTs rarely spread to the lymph nodes.
• Metastasis (M) indicates if cancer has spread to other parts of the body. The most common sites of spread are the liver, bones, lungs, and the tissue layers lining the inside of the abdomen.
• Mitotic rate is a lab test measurement of how fast the cancer cells are growing and dividing. It is described as either low or high. A low mitotic rate predicts a better outcome.

Numbers or letters after T, N, and M provide more details about each of these factors. Higher numbers mean the cancer is more advanced.

Stage grouping

Once a person’s T, N, and M categories have been determined, this information is combined in a process called stage grouping to assign an overall stage.

Although the T, N, and M categories are the same for all GISTs, there are 2 different stage grouping schemes, depending on where the cancer starts:

• The stomach or the omentum (an apron-like layer of fatty tissue that hangs over the organs in the abdomen)
• The small intestine, esophagus, colon, rectum, or peritoneum (a layer of tissue that lines the organs and walls of the abdomen).

This is because GISTs that start in the stomach or omentum are typically less likely to grow and spread to other parts of the body than GISTs starting in other locations.

The stages for GISTs range from I through IV. As a rule, the lower the number, the less the cancer has spread.

Although each person’s cancer experience is unique, cancers with similar stages tend to have a similar outlook and are often treated in much the same way.

Cancer staging can be complex, so ask your doctor to explain it to you in a way you understand.