TNM and number stages of bowel cancer

The stage of a cancer means how big it is and whether it has spread. The tests and scans you have when diagnosing your cancer give some information about the stage. It is important because treatment is often based on the stage of a cancer. Many doctors in the UK now use the 5th version of the TNM stages or the number stages of bowel cancer. These stages are used across the world. Some doctors use the Dukes' staging system, which is described on the next page.

TNM stands for Tumour, Node, Metastases. This staging system describes the size of a primary tumour (T), whether any lymph nodes contain cancer cells (N), and whether the cancer has spread to another part of the body (M).

There are 4 stages of tumour size in bowel cancer

• 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 into the outer lining of the bowel wall or into organs or body structures next to the bowel
• T4 means the tumour has grown into other parts of the bowel, other organs or body structures near to the bowel (such as the liver or small bowel), or the tumour has broken through the membrane covering the outside of the bowel (the peritoneum)

There are 3 possible stages describing whether cancer cells are in the lymph nodes

• N0 means there are no lymph nodes containing cancer cells
• N1 means that 1 to 3 lymph nodes close to the bowel contain cancer cells
• N2 means there are cancer cells in 4 or more lymph nodes that are further than 3cm away from the main tumour in the bowel or there are cancer cells in lymph nodes connected to the main blood vessels around the bowel

There are two 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

The number system uses the TNM stages to group bowel cancers. There are 5 main stages in this system. They are

• Stage 0 or carcinoma in situ
• Stage 1
• Stage 2
• Stage 3
• Stage 4

Stage 0 or carcinoma in situ (CIS)

If you are told you have CIS or stage 0 colorectal cancer, there are cancer cells in your bowel lining. But all the cancer cells are contained within the lining of the bowel. So there is very little risk of any cancer cells having spread.

Stage 1

This means the cancer has grown through the inner lining of the bowel, or into the muscle wall, but no further. There is no cancer in the lymph nodes (T1, N0, M0 or T2, N0, M0).

Stage 2

This stage is divided into 2a and 2b

• Stage 2a means that there are no cancer cells in the lymph nodes but the cancer has broken through the outer covering of the bowel (T3, N0, M0)
• Stage 2b means that the cancer has grown through the outer covering of the bowel wall and into tissues or organs next to the bowel (T4). But no lymph nodes are affected (N0) and the cancer has not spread to another area of the body (M0).

Stage 3

Stage 3 is divided into 3 stages

• Stage 3a means that the cancer is still in the inner layer of the bowel wall or has grown into the muscle layer, and between 1 and 3 nearby lymph nodes contain cancer cells (T1, N1, M0 or T2, N1, M0)
• Stage 3b means that the cancer has grown through the bowel wall or into surrounding body tissues or organs and between 1 and 3 nearby lymph nodes contain cancer cells (T3, N1, M0 or T4, N1, M0)
• Stage 3c means that the cancer can be any size, has spread to 4 or more nearby lymph nodes, but there is no cancer spread to any other part of the body (any T, N2, M0)

Stage 4

This means your cancer has spread to other parts of the body (such as the liver or lungs) through the lymphatic system or bloodstream (any T, any N, M1).