How Does Bowel Cancer Staging Work?

Staging bowel cancer involves describing its size, its location, and the extent to which it has spread. If you have surgery, your doctor will grade the cancer by examining the cells under a microscope.

There are various methods of staging bowel cancer.  These include:

• The TNM system
• The Number Staging System, and the
• Dukes' system

The TNM System of Staging

This system of staging describes the amount and spread of cancer in a patient's body.

• T describes the size of the tumour and any spread of cancer into surrounding tissues
• N describes the spread of cancer to nearby lymph nodes, and
• M describes the level of metastasis (spread of cancer to other parts of the body)

Bowel tumours progress through four levels, namely:

• T1 – the tumour is only located in the inner layer of the bowel
• T2 – the tumour has grown into the muscle layer of the bowel wall
• T3 – the tumour has grown into the outer lining of the bowel wall
• T4 – the tumour has grown through the outer lining of the bowel wall

The progression of cancer to the lymph nodes is monitored in three levels, namely:

• N0 – no lymph nodes contain cancer cells
• N1 – cancer cells in up to three nearby lymph nodes
• N2 – cancer cells in four or more nearby lymph nodes

M (metastases) indicates whether the cancer has spread, or metastasised, to other parts of the body. There are two levels, namely:

• M0 – the cancer has not spread to other parts of the body.
• M1 – the cancer has spread to other parts of the body, like the lungs or liver.

An example of a diagnosis using this method may be 'T3N1M0'. This means the cancer has grown into the outer lining of the bowel and has spread into a maximum of three nearby lymph nodes. It has not spread to other parts of the body.

Number staging

Information gathered from the TNM staging report can be used to give a number stage between 1 and 4.

Stage 1

The cancer is confined to the inner part of the bowel and it has not spread outside the bowel wall.

Stage 2

The cancer has grown into or through the outer layer of the bowel wall. Stage 2 has three levels of cancer progression, namely:

• Stage 2A means that the cancer has grown into the outer lining of the bowel
• Stage 2B means that the cancer has grown through the outer lining of the bowel into the tissue layer (peritoneum) covering the organs in the abdomen, and
• Stage 2C means that the cancer has grown through the wall of the bowel, into organs and tissues next to it.

Stage 3

The cancer has spread to nearby lymph nodes. Three levels of cancer progression are seen in Stage 3, namely:

• Stage 3A - the cancer is still in the inner (muscle) layer of the bowel wall, and it has spread to between 1 to 3 nearby lymph nodes or to areas of tissue close to the lymph nodes.
• Stage 3B means that the cancer has grown into the outer lining of the bowel wall or into the tissue layer covering the organs in the abdomen and it has spread to between 1 and 3 nearby lymph nodes or to areas of fat adjacent to the lymph nodes. During this stage, the cancer could still be in the inner layer of the bowel wall, and it has spread to 7 or more nearby lymph nodes.
• Stage 3C means that the cancer has grown through the outer lining of the bowel wall into the tissue layer covering the organs in the abdomen and between 4 to 7 nearby lymph nodes contain cancer. During this stage, the cancer may grow through the bowel wall into other nearby organs and spread to at least one nearby lymph node or to areas of fat close to the lymph nodes.

Stage 4

The cancer has spread to other parts of the body through the lymphatic system or the bloodstream. Three levels of cancer progression are seen in Stage 4, namely:

• Stage 4A means that the cancer has spread to 1 distant site or organ, but it has not spread to the tissue lining your abdomen (peritoneum).
• Stage 4B means that the cancer has spread to 2 or more distant organs, but not to the tissue lining your peritoneum.
• Stage 4C means that the cancer has spread to other distant organs and it has spread to the lining of your peritoneum.

Dukes' System

Doctors occasionally use the Dukes’ system to describe the stages of bowel cancer. Your bowel cancer may be described as Dukes' A, B, C or D. The Dukes’ system of grading ties in with the TNM and number staging methods of grading. The system is graded from A to D:

Dukes' A 

The cancer has only grown into the inner layer or muscle layer of the bowel wall. It has not spread to the lymph nodes or other parts of the body. This grading equates to Stage 1 and TNM stage 1 (T1, N0, M0 or T2, N0, M0)

Dukes' B 

The cancer has grown through the muscle layer or outer layer and might be growing into surrounding tissues adjacent to the bowel. It has not spread to the lymph nodes or other parts of the body (it has not metastasised). This grading equates to Stage 2 and TNM stage 2 (T3, N0, M0 or T4, N0, M0).

Dukes' C

The cancer has spread to nearby lymph nodes, but it has not spread to other parts of the body. This grading equates to Stage 3 and TNM stage 3 (Any T, N1 or N2, M0).

Dukes' D

The cancer may or may not have spread to nearby lymph nodes but it has spread to other parts of the body, such as the liver or lungs, i.e. it has metastasised. This grading equates to Stage 4 and TNM stage 4 (Any T, any N, M1).

Grading Bowel Cancer

Grading bowel cancer assists in showing us how likely it is to spread and at what rate. It gives your doctor an idea of how your cancer might progress and the correct treatment plan. A low grade cancer, for example, would most probably grow more slowly and is less likely to spread than a high grade cancer. The following three grades of cancer are recognised:

Grade 1 (Low Grade)

The cancer cells look similar to normal cells, i.e. they are well differentiated.

Grade 2 (Moderate Grade)

The cancer cells look more abnormal  and are moderately differentiated

Grade 3 (High Grade)

The cancer cells look very abnormal and are poorly differentiated. This grade of cancer is usually fast-growing.