Staging is the process of finding out how far a cancer has spread. For many cancers, the stage is an important factor in selecting treatment options and in predicting the patient's prognosis (the outlook). To help stage the tumor, doctors use the results of physical exams and imaging, endoscopy, or other tests, such as those described in "How are gastrointestinal stromal tumors diagnosed?".
AJCC TNM staging system
Doctors describe the extent of spread of most types of cancer by using a staging system. The most common system used is the TNM system of the American Joint Committee on Cancer (AJCC). The AJCC recently developed a TNM staging system for gastrointestinal stromal tumors (GISTs). This system contains 4 key pieces of information:
- T describes the size of the primary tumor, measured in centimeters (cm).
- N describes whether the cancer has spread to nearby (regional) lymph nodes (which is very rare for GISTs).
- M indicates whether the cancer has metastasized (spread) to other organs of the body. If a GIST does spread, most often it is within the abdomen, such as to the liver. Less often, it may spread to the lungs and bones.
- The mitotic rate is a measure 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 appear after T, N, and M to provide more details about each of these factors:
- The numbers 0 through 4 indicate increasing severity.
- The letter X means "cannot be assessed" because the information is not available.
T categories for GIST
TX: The primary (main) tumor cannot be assessed.
T0: No signs of a primary tumor.
T1: The tumor is 2 cm or less across (about 4/5 of an inch).
T2: The tumor is larger than 2 cm across but not larger than 5 cm (about 2 inches).
T3: The tumor is larger than 5 cm across but not larger than 10 cm (about 4 inches).
T4: The tumor is larger than 10 cm across in size.
N categories for GIST
NX: Regional (nearby) lymph nodes cannot be assessed.
N0: The cancer has not spread to nearby lymph nodes.
N1: The cancer has spread to nearby lymph nodes.
M categories for GIST
M0: The cancer has not spread (metastasized) to distant organs or sites.
M1: The cancer has spread to distant organs or sites (like the liver or the lungs).
Stage grouping
Once the T, N, and M categories have been determined, this information is combined, along with the mitotic rate, in a process called stage grouping. The overall stage is expressed in Roman numerals from I (the least advanced) to IV (the most advanced). The stage grouping is a bit different depending on where the tumor starts.
Stage grouping for GIST that starts in the stomach or the omentum*
*The omentum is an apron-like layer of fatty tissue that hangs over the organs in the abdomen
Stage IA: T1 or T2, N0, M0, low mitotic rate: The tumor is no larger than 5 cm across (T1 or T2). The cancer has not spread to nearby lymph nodes (N0) or distant sites (M0). The mitotic rate is low.
Stage IB: T3, N0, M0, low mitotic rate: The tumor is larger than 5 cm but not larger than 10 cm across (T3). The cancer has not spread to nearby lymph nodes (N0) or distant sites (M0). The mitotic rate is low.
Stage II: One of the following applies:
T1 or T2, N0, M0, high mitotic rate: The tumor is no larger than 5 cm across (T1 or T2). The cancer has not spread to nearby lymph nodes (N0) or distant sites (M0). The mitotic rate is high.
T4, N0, M0, low mitotic rate: The tumor is larger than 10 cm across (T4). The cancer has not spread to nearby lymph nodes (N0) or distant sites (M0). The mitotic rate is low.
Stage IIIA: T3, N0, M0, high mitotic rate: The tumor is larger than 5 cm but not larger than 10 cm across (T3). The cancer has not spread to nearby lymph nodes (N0) or distant sites (M0). The mitotic rate is high.
Stage IIIB: T4, N0, M0, high mitotic rate: The tumor is larger than 10 cm across (T4). The cancer has not spread to nearby lymph nodes (N0) or distant sites (M0). The mitotic rate is high.
Stage IV: One of the following applies:
Any T, N1, M0, any mitotic rate: The tumor can be any size (any T) and the cancer has spread to nearby lymph nodes (N1). It has not spread to distant sites (M0). The tumor can have any mitotic rate.
Any T, any N, M1, any mitotic rate: The tumor can be any size (any T) and it may or may not have spread to nearby lymph nodes (any N). The cancer has spread to distant sites, such as the liver or the lungs (M1). The tumor can have any mitotic rate.
Stage grouping for GIST of the small intestine, esophagus, colon, rectum, and peritoneum**
**The peritoneum is a layer of tissue that lines the organs and walls of the abdomen.
Tumors in these locations are more likely to grow quickly than GISTs that start in the stomach.
Stage I: T1 or T2, N0, M0, low mitotic rate: The tumor is no larger than 5 cm across (T1 or T2). The cancer has not spread to nearby lymph nodes (N0) or distant sites (M0). The mitotic rate is low.
Stage II: T3, N0, M0, low mitotic rate: The tumor is larger than 5 cm but not larger than 10 cm across (T3). The cancer has not spread to nearby lymph nodes (N0) or distant sites (M0). The mitotic rate is low.
Stage IIIA: One of the following applies:
T1, N0, M0, high mitotic rate: The tumor is no larger than 2 cm across (T1). The cancer has not spread to nearby lymph nodes (N0) or distant sites (M0). The mitotic rate is high.
T4, N0, M0, low mitotic rate: The tumor is larger than 10 cm across (T4). The cancer has not spread to nearby lymph nodes (N0) or distant sites (M0). The mitotic rate is low.
Stage IIIB: T2 to T4, N0, M0, high mitotic rate: The tumor is larger than 2 cm across (T2 to T4). The cancer has not spread to nearby lymph nodes (N0) or distant sites (M0). The mitotic rate is high.
Stage IV: One of the following applies:
Any T, N1, M0, any mitotic rate: The tumor can be any size (any T) and the cancer has spread to nearby lymph nodes (N1). It has not spread to distant sites (M0). The tumor can have any mitotic rate.
Any T, any N, M1, any mitotic rate: The tumor can be any size (any T) and it may or may not have spread to nearby lymph nodes (any N). The cancer has spread to distant sites, such as the liver or the lungs (M1). The tumor can have any mitotic rate.
Feedback
