TNM staging for bowel cancer

Tumour, node and metastasis (TNM) staging is one of the systems used to stage bowel (colon and rectal) cancer.

The stage of a cancer tells you how big it is and how far it has spread. It helps your doctor decide which treatment you need.

Doctors may also use the number staging system. The Dukes staging system is rarely used anymore. 

Tumour (T)

Tumour describes the size of the tumour. This is a simplified description of the T stage.

Tis means carcinoma in situ. The cancer is at its earliest stage and only in the bowel lining (mucosa).

T1 means the tumour is only in the inner layer of the bowel.

T2 means the tumour has grown into the muscle layer of the bowel wall.

T3 means the tumour has grown through the muscle layer of the bowel wall and into the tissues surrounding the bowel. It has not gone through the tissue layer covering the outside of the bowel (peritoneum).

T4 is split into 2 stages, T4a and T4b:

• T4a means the tumour has grown through the outer lining of the bowel wall and has spread into the tissue layer (peritoneum) covering the organs in the tummy (abdomen)
• T4b means the tumour has grown through the bowel wall into nearby organs

Node (N)

Node (N) describes whether the cancer has spread to the lymph nodes.

There are 3 possible stages describing whether cancer cells are in the lymph nodes – N0, N1 and N2:

N0 means there are no lymph nodes containing cancer cells.

N1 is split into 3 stages – N1a, N1b and N1c:

• N1a means there are cancer cells in 1 nearby lymph node
• N1b means there are cancer cells in 2 or 3 nearby lymph nodes
• N1c means the nearby lymph nodes don’t contain cancer, but there are cancer cells in tissue near the tumour. These cancer cells are separate from the main tumour.

N2 is split into 2 stages – N2a and N2b:

• N2a means there are cancer cells in 4 to 6 nearby lymph nodes
• N2b means there are cancer cells in more than 7 nearby lymph nodes

Metastasis (M)

Metastasis (M) describes whether the cancer has spread to a different part of the body.

There are 2 stages of cancer spread (metastasis):

M0 means the cancer has not spread to other organs.

M1 means the cancer has spread to other parts of the body such as the lung or liver. It is split into 3 stages, M1a, M1b and M1c:

• M1a means the cancer has spread to 1 distant site or organ, for example the liver, but it hasn’t spread to the tissue lining your tummy (peritoneum)

• M1b means the cancer has spread to 2 or more distant sites or organs, but it hasn’t spread to the tissue lining your peritoneum

• M1c means the cancer may have spread to distant organs and it has spread to your peritoneum

Treatment

The stage of your cancer helps your doctor to decide which treatment you need. Treatment also depends on:

• your type of cancer (the type of cells the cancer started in)
• where the cancer is in your bowel (colon or rectum)
• other health conditions that you have

The stage of the cancer and these other factors can also give an idea of your outlook (prognosis).

The main treatments for cancer of the large bowel (colon cancer) are:

• surgery
• chemotherapy

The main treatments for cancer of the back passage (rectal cancer) are:

• surgery
• radiotherapy
• chemotherapy
• chemotherapy and radiotherapy together (chemoradiotherapy)

For bowel cancer that has spread (advanced cancer) you might have these treatments as well as:

•    a targeted drug
•    immunotherapy