After colon cancer is diagnosed, the doctors use colon cancer staging system to find the extent of cancer spread in the body. Colon cancer staging is very important because the treatment and the recovery largely depend on the stage of colon cancer. For cancer in its early stages, surgery may be all that is needed. But for more advanced cancer, other treatments like radiation or chemotherapy may be used. Thus, colon cancer staging systems can help save lives by early diagnosis of the current cancer stage.
Colon cancer staging is the process of finding out how far the colon cancer has spread. It is based on the outcome of physical examination, biopsies, and imaging tests like CT or MRI scan, x-rays or PET scan. Colon cancer is one of the most deadliest cancers, and a proper colon cancer staging system is in place in all hospitals to help with the proper diagnosis.
There are actually 2 types of colon cancer staging.
- The clinical stage, where the doctor estimate of the extent of the disease based on the result of physical exam, biopsy and any other imaging tests.
- If the patient had undergone a surgery, the doctor may also determine the pathologic stage, which is often based on the same factors as the clinical stage, and what is found as a result of surgery.
In some cases, the clinical and pathologic stages may be different. For example, during surgery, the doctor may find the cancer spread on an area that did not show up on any imaging tests, which gives the cancer a more advanced pathologic stage. Most patients with colon cancer undergo surgery, so the pathologic stage is often used in describing the extent of this cancer. Pathologic staging is likely to be the most accurate colon cancer staging process than clinical staging, as it allows the doctor to get a firsthand impression on the extent of the disease.
AJCC (TNM) Colon Cancer Staging System
The most commonly used colon cancer staging system for this type of cancer is the American Joint Committee on Cancer (AJCC), which is also known as the TNM system. The TNM colon cancer staging system describes 3 key pieces of information, which include:
- T, which describes how far the primary tumor has grown into the intestinal wall and whether it has grown into the nearby areas.
- N, which describes the extent of spread of cancer to the nearby lymph nodes. Lymph nodes are small immune system cells that are very important in fighting infections.
- M, which describes whether the colon cancer has spread (metastasized) to other organs in the body.
The numbers or letters that follows T, N, and M provide more details about each of these factors. The numbers 0 through 4 indicates the increasing severity of cancer. The letter X means that ” it cannot be assessed because of lack of information.” This is where the colon cancer staging needs more tests ran for an accurate diagnosis.
T categories for colon cancer
The T categories of colon cancer staging describe the extent of spread of cancer through the layers of the wall of the colon. These layers include:
- The inner lining of the mucosa
- Muscularis mucosa, the thin muscle layer
- Submucosa, the fibrous tissue beneath this muscle layer
- A thick muscle layer, the muscularis propria that usually contracts to force the contents of the intestines along
- The thin, outermost layers of connective tissue (subserosa and serosa) which covers most of the colon
Tx means, due to lack of information the description on the extend of tumor is not possible.
Tis means that the colon cancer is in its earliest stage. It involves only the mucosa and has not spread beyond the muscularis mucosa.
T1 means that the colon cancer has grown through the muscularis mucosa and also extends into the submucosa.
T2 means the colon cancer has grown through submucosa into the muscularis propria.
T3 means that the colon cancer has spread through muscularis propria and also into the outermost layers of the colon.
T4a means that the cancer has grown through the serosa which is the outermost intestinal lining.
T4b means that the cancer has grown through the wall of the colon and is attached to or invades into the nearby tissues or organs.
N categories for colorectal cancer
The N categories in colon cancer staging denotes whether or not the colon cancer has spread into the nearby lymph nodes and, if so, the number of lymph nodes that are involved. To get a precise idea about the lymph node involvement, most physicians recommend that at least 12 lymph nodes be removed at the time of surgery and looked at under a microscope. This helps assist with a colon cancer staging diagnosis.
Nx means that due to lack of information, the description of lymph node involvement is not possible.
N0 means there is no cancer spread in the nearby lymph nodes.
N1 means that cancer cells are found in or near 1 to 3 lymph nodes.
N1a means that cancer cells are found in nearby 1 lymph node.
N1b means that cancer cells are found in nearby 2 to 3 lymph nodes.
N1c means small deposits of cancer cells are found in the areas of fat near to the lymph nodes, but not actually in the lymph nodes.
N2 means that cancer cells are found in nearby 4 or more lymph nodes
N2a means that cancer cells are found in nearby 4 to 6 lymph nodes.
N2b means that cancer cells are found in nearby 7 or more lymph nodes.
M categories for colorectal cancer
M categories of colon cancer staging indicate whether or not the cancer has spread to distant organs like the lungs, liver or distant lymph nodes.
M0 means no distant spread is found.
M1a means it has spread to 1 distant organ or a set of distant lymph nodes.
M1b indicates that the cancer has spread to more than 1 distant organ or a set of distant lymph nodes, or it has spread to very distant parts of the peritoneum.
Stage grouping
When the T, N, and M categories of colon cancer staging have been determined, the information is combined in a process called the stage grouping. The stage is denoted in Roman numerals from stage I (the least advanced) to stage IV (the most advanced). Some stages are also subdivided with letters. The stages include
- Stage 0 Colon Cancer: This is the earliest stage in colon cancer staging and is called carcinoma in situ. “Carcinoma” means cancer that starts in epithelial tissue and “in situ” means the original position. Colon cancer is considered as stage 0 when it has not moved from where it started; it is confined to the innermost lining of the colon.
- Stage 1 Colon Cancer: During this stage, cancer has extended into the middle layers of the colon. Stage 1 is usually called Duke’s A colon cancer.
- Stage 2 Colon Cancer: This stage is Duke’s B colon cancer. Colon cancer is considered stage 2 once it moves beyond the middle layers. Sometimes it is still considered as stage 2 even after it has extended into the nearby organs.
- Stage 3 Colon Cancer: Colon cancer found at least in three lymph nodes is referred to as stage 3, which is formerly called Duke’s C colon cancer.
- Stage 4 Colon Cancer: This is formerly referred to as the Duke’s D colon cancer. It is the most advanced colon cancer stage. In stage 4 colon cancer, it has spread to the nearby lymph nodes and other organs in the body like liver and the lungs.
Colon cancer staging helps the physician know the exact condition of the patient and the chances of survival. A person suffering from the most advanced type of cancer may not have good chances of surviving it through the end, but proper diagnosis through the colon cancer staging process helps to be extremely advantageous in getting the proper treatment.
