Following a diagnosis of colon cancer, your doctor will determine the stage of cancer so that an ideal treatment plan can be formulated. Staging gives information about the size of the tumor, its location, whether it has spread to other regions of the body, and how far.
The stage of the cancer is determined by examination and diagnostic tests. Your doctor may recommend a CT scan, MRI, endorectal ultrasound study, biopsy, and certain blood tests.
Staging of colon cancer is usually done using the TNM system which takes 3 factors into consideration:
- T stands for tumor
- N stands for nodes
- M stands for metastasis
Each letter has a number next to it denoting its value for eg: T2, N1, or M0. The higher the value the more severe is cancer.
The value of T determines the size of the main tumor and how much it has infiltrated into the wall of the colon.
The value of N determines the number of lymph nodes that the tumor has spread to.
The value of M determines how far the cancer has spread to other organs of the body.
The values of all 3 factors are combined to determine the stage of your cancer. Colon cancer is described as having five stages: 0, I, II, III, IV. Certain stages are divided into substages denoted by letters next to the numbers such as IIA, IIIB, etc.
Stage 0 (Carcinoma in situ)
Abnormal cells which may turn cancerous are noted in the innermost lining cells (mucosa) of the colon.
Cancer cells are found in both the inner and second layer of the lining mucosa (submucosa) of the colon. Cancer may also have spread to the next layer or the muscular layer but no lymph nodes are involved.
This stage has 3 substages:
- Stage IIA: The cancer has spread to reach the outermost layer of the colon wall but has not grown out of this layer.
- Stage IIB: The cancer has grown beyond the outermost layer of the colon wall but has not infiltrated the adjacent structures such as the peritoneal layer which closely surrounds the abdominal organs.
- Stage IIC: The cancer has spread to the peritoneum and other nearby structures.
In this stage, the cancer has spread to the lymph nodes. It has 3 substages:
- Stage IIIA: Cancer is found in the nearby lymph nodes after penetrating through all the layers of the colon and involving the nearby structures.
- Stage IIIB: Cancer has spread through the colon wall and is found in up to 3 nearby lymph nodes.
- Stage IIIC: Four or more nearby lymph nodes are involved but the cancer has not metastasized (spread to distant sites).
This is an advanced stage in which the cancer has spread to distant sites. It has 2 substages:
- Stage IVA: The cancer has spread to one distant site such as the lung or liver.
- Stage IVB: The cancer has spread to 2 or more distant sites.