Staging and grading

The stage of a cancer means how big it is and whether it has spread. The tests and scans you have had to diagnose bowel cancer will tell your doctors more about the stage of the cancer. This is important because treatment decisions may be based on this stage.

Doctors mostly use the TNM staging system to describe the stage of the cancer. This records information about how far the tumour has grown into the bowel and whether it has spread into nearby lymph nodes or distant organs. Information from the TNM system can also be used to give a numbered stage, showing how far the cancer may have spread on a scale of 0–4.

Doctors will also want to know the grade of the cancer. This will give them an idea of how quickly the cancer may grow. They will examine the cancer cells under a microscope and compare how they look to normal cells. If they look very different, the cancer may be a higher grade and so grow more quickly.

Staging

The stage of a cancer describes its size and whether it has spread. The grade of a cancer gives an idea of how quickly it may develop. Knowing the stage of your cancer helps doctors decide on the best treatment for you. The most commonly used staging system is the TNM system.

TNM staging system

T describes how far the tumour has grown into the wall of the bowel, and whether it has grown into nearby tissues or organs.

N describes whether the cancer has spread to the lymph nodes.

M describes whether the cancer has spread to another part of the body such as the liver or lungs (secondary or metastatic cancer).

T – Tumour

The bowel wall is made up of layers of different tissues (see diagram below).

Tis means the cancer is at its earliest stage (in situ). It is growing into the mucosa but no further.

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

T2 means the tumour has grown into the muscle layer of the bowel wall but no further.

T3 means the tumour has grown into the outer lining of the bowel wall (serosa) but no further.

T4 means the tumour has grown through the outer layer of the bowel wall (serosa) and through the membrane covering the outside of the bowel wall (peritoneum).

  • T4a means it has grown into other nearby structures, such as other parts of the bowel or other organs or body structures.
  • T4b means the tumour has caused a hole in the bowel wall (perforation) and cancer cells have spread outside the bowel.

Cross-section showing the different layers of the bowel and the different T stages of cancer (in purple)
Cross-section showing the different layers of the bowel and the different T stages of cancer (in purple)

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N – Nodes

N0 means no lymph nodes contain cancer cells.

N1 means there are cancer cells in up to three nearby lymph nodes.

N2 means there are cancer cells in four or more nearby lymph nodes.

M – Metastases

M0 means the cancer hasn’t spread to distant organs.

M1 means the cancer has spread to distant organs such as the liver or lungs.

Number staging system

Information from the TNM system can be used to give a number stage from 0 to 4.

Stage 0

The cancer is at its earliest stage and is only in the mucosa (Tis N0 M0).

Stage 1

The cancer has grown into the submucosa or muscle but has not spread to the lymph nodes or elsewhere (T1 N0 M0 or T2 N0 M0).

Stage 2

The cancer has grown through the muscle wall or through the outer layer of the bowel, and may be growing into tissues nearby. The cancer has not spread to the lymph nodes or elsewhere (T3 N0 M0 or T4 N0 M0).

Stage 3

The tumour is any size and has spread to lymph nodes nearby, but has not spread anywhere else in the body (Any T N1 or N2 M0).

Stage 4

The tumour is any size. It may have spread to nearby lymph nodes. The cancer has spread to other parts of the body such as the liver or lungs (Any T Any N M1).


Grading

The grade of a cancer gives doctors an idea of how quickly it may develop. Doctors will look at a sample of the cancer cells under a microscope to find the grade of your cancer.

Grade 1 (low-grade)

The cancer cells tend to grow slowly and look quite similar to normal cells (they are ‘well differentiated’). These cancers are less likely to spread than higher grade cancers.

Grade 2 (moderate-grade)

The cancer cells look more abnormal.

Grade 3 (high-grade)

The cancer cells tend to grow more quickly and look very abnormal (they are ‘poorly differentiated’). These cancers are more likely to spread than low-grade cancers.

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