The colon cancer staging is done based on the TNM system of staging.

The TNM system of staging has the following factors:

Tumor (T): This depends on how far the cancer has grown into the wall of the colon. These layers include, the mucosa which is the inner lining, the sub mucosa which is the fibrous tissue below the muscle, the muscularis propria which is a thick muscle layer and the serosa and suberosa which are a thin layer of connective tissue.

Lymph node s (N): This factor indicates if the cancer has spread to the lymph nodes

Metastasis (M): This factor refers to whether the cancer has spread to other parts of the body.
Stage 4 colon cancer can further be classified into stage 4A, 4B and 4C

In stage 4 colon cancer, the diagnosis for the substages is done according to the following TNM categories:

Stage 4A

Any T:
The cancer may or may not have grown through the wall of the colon or rectum.

Any N:
The cancer might or might not have spread to the nearby lymph nodes

M1a:
The cancer has spread to 1 distant organ such as the liver or lungs or has spread to a distant set of lymph nodes but has not spread to distant parts of the peritoneum which is the lining of the abdominal cavity.

Stage 4B

Any T:
The cancer may or may not have grown through the wall of the colon or rectum.

Any N:
The cancer might or might not have spread to the nearby lymph nodes

M1b:
The cancer has spread to more than 1 distant organ such as the liver or lungs or has spread to a distant set of lymph nodes but has not spread to distant parts of the peritoneum which is the lining of the abdominal cavity.

Stage 4C

Any T:
The cancer may or may not have grown through the wall of the colon or rectum.

Any N:
The cancer might or might not have spread to the nearby lymph nodes.

M1c:
The cancer has spread to distant parts of the peritoneum which is the lining of the abdominal cavity and it may or may not have spread to distant organs or lymph nodes.


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