Staging and grading of colon and rectal cancer

The stage of a cancer describes its size and whether it has spread beyond its original area of the body. Knowing the extent of the cancer helps the doctors decide on the most appropriate treatment.

Grading| refers to the appearance of the cancer cells under the microscope. The grade gives an idea how quickly they may develop.

Staging systems Back to top

The exact stage of a colon or rectal cancer can often only be determined after surgery, when the pathologists can examine the cancer and the piece of healthy colon or rectum that has been removed.

Generally, colon and rectal cancers are divided into four stages, ranging from small and localised to cancer that has spread to other parts of the body. If the cancer has spread, this is known as secondary or metastatic cancer. If the cancer comes back after initial treatment it’s known as recurrent cancer.

There are two different staging systems used to stage colon and rectal cancer. The first system, called the Dukes staging system, is gradually being replaced by the TNM staging system, which gives more detailed information.

The Dukes staging system Back to top

Dukes A The cancer is contained within the bowel wall.

Dukes B The cancer has spread through the muscle of the bowel wall, but the lymph nodes are not affected.

Dukes C The cancer has spread to one or more of the lymph nodes close to the bowel. Lymph nodes are usually the first place the cancer spreads to.

Dukes D The cancer has spread to another part of the body such as the liver or the lungs (secondary cancer).  

TNM staging system Back to top

TNM stands for T umour, N ode and M etastases.

• T describes the tumour and if it has spread into the bowel wall.
• 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 the lungs (secondary or metastatic cancer).

Tumour

There are four levels used to describe the tumour:

T1 The tumour is only in the inner layer of the colon or rectum.

T2 The tumour has begun to grow into the muscle layer of the colon or rectum, but not all the way through it.

T3 The tumour has grown through the muscle layer or into structures next to the bowel.

T4 The tumour has broken through the outer covering of the bowel, or spread to other parts of the bowel, or other organs or structures close to the bowel.

Nodes

There are three levels describing whether the lymph nodes are affected:

N0 No lymph nodes are affected.

N1 Between one and three lymph nodes close to the colon or rectum (regional nodes) are affected.

N2 The cancer has been found in four or more regional nodes. 

Metastases

There are two different levels to describe whether the cancer has spread to other parts of the body (metastases):

M0 The cancer hasn’t spread to other parts of the body.

M1 The cancer has spread to other parts of the body. 

Number stages

To make it easier to understand the TNM system, doctors often combine the information about the tumour, the lymph nodes and whether the cancer has spread into stage groups:  

Stage 0 – The cancer is in the very earliest stage and is only in the inner lining of the colon or rectum. This stage is sometimes called carcinoma in situ.

Stage 1 – The cancer is affecting the inner lining of the colon or rectum, or has begun to grow into the muscle, but no further. No lymph nodes are affected (T1, N0, M0 or T2, N0, M0).

Stage 2A – The cancer has grown through the outer muscle layer of the colon or rectum, but has not spread to nearby structures or to any lymph nodes or other parts of the body (T3, N0, M0).

Stage 2B – The cancer has spread through the outer muscle layer of the colon or rectum and into nearby structures, but it’s not affecting any lymph nodes or other parts of the body (T4, N0, M0).

Stage 3A – The cancer is affecting the inner lining of the colon or rectum, or has begun to grow into the muscle, and is affecting between one and three lymph nodes close to the colon. It has not spread to other parts of the body (T1, N1, M0 or T2, N1, M0).

Stage 3B – The cancer has grown through the outer layer of the colon or rectum, or into nearby structures, and is affecting between one and three lymph nodes (T3, N1, M0 or T4, N1, M0).

Stage 3C – The cancer may or may not have grown through the wall of the colon or rectum, but is affecting four or more nearby lymph nodes. It has not spread to other parts of the body (Any T, N2, M0).

Stage 4 – The cancer may or may not have grown through the wall of the colon or rectum, may or may not have spread to nearby lymph nodes, but has spread to other parts of the body, such as the liver or lungs (Any T, Any N, M1).

Grading Back to top

There are three grades: grade 1 (low-grade), grade 2 (moderate- or intermediate- grade) and grade 3 (high-grade).

Low-grade means that the cancer cells look very like the normal cells of the bowel (the cells are sometimes described as being well differentiated). They are usually slow-growing and are less likely to spread.

In high-grade cancers the cells look very abnormal (the cells are poorly differentiated). They are likely to grow more quickly and are more likely to spread.

Moderate-grade cancers fall between these two grades and have a level of activity somewhere in between. They are sometimes described as being moderately differentiated.