What is bowel cancer

What is bowel cancer?

The bowel is part of the digestive system. It is divided in two:
• The small bowel; and
• The large bowel.
The food we eat ends up in the large bowel. Here, water and some nutrients are absorbed, leaving waste. Waste passes through the rest of the large bowel before leaving the body.
Bowel cancer includes cancers of the large bowel and back passage (rectum).

The bowel is part of the digestive system. It is divided in two:

  • The small bowel; and
  • The large bowel.

The food we eat ends up in the large bowel. Here, water and some nutrients are absorbed, leaving waste. Waste passes through the rest of the large bowel before leaving the body.

 

The bowel- also known as the colon

Symptoms of bowel cancer

The symptoms of bowel cancer can include:

  • Bleeding from the back passage or blood in your poo;
  • A change in normal bowel habits;
  • A lump that your doctor can feel in your back passage or abdomen (more commonly on the right side);
  • A feeling of needing to strain in your back passage (as if you need to pass a bowel motion), even after opening your bowels;
  • Losing weight;
  • Pain in your abdomen or back passage; or
  • A lower than normal level of red blood cells (anaemia).

The ‘stages’ of bowel cancer

The ‘stage’ of a cancer means how big it is and whether or not it has spread. This is important because treatment is often based on the stage of a cancer.

Diagnosing the stage of cancer

‘Clinical’ stage testing

The tests and scans you have when diagnosing your cancer gives information about the ‘clinical’ stage.

‘Pathologic’ stage testing

During surgery the doctor finds out more about the cancer. The tissue the surgeon removes, including the lymph nodes, is carefully examined in the laboratory. These results are combined with the clinical stage to give a ‘pathological’ stage. This is more accurate than the clinical stage.

The pathological stage may be different to the clinical stage. For example, the surgeon may find that the cancer is more advanced than it looked on the scans.

On your staging report, you may see a lower case letter (c or p) written before the stage. This shows that it is the clinical or pathological stage.

TNM staging system

Your doctor will then decide what ‘stage’ your cancer is at using the ‘TNM’ staging system. TNM stands for:

  • Tumour
  • Node
  • Metastasis 

The TNM staging system describes:

  • The size of a primary tumour (T);
  • If any lymph nodes contain cancer cells (N); and
  • If the cancer has spread to another part of the body (there is metastasis) – 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; and
  • T4 means the tumour has grown through the outer lining of the bowel wall.

At stage T4, the tumour may have grown into another part of the bowel, or other nearby organs or structures. Or it may have broken through the membrane covering the outside of the bowel (the peritoneum). See Figure 1: the T stages of bowel cancer.

 

N – Lymph nodes

There are 3 possible stages describing whether or not 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; and
  • N2 means there are cancer cells in 4 or more nearby lymph nodes.

M – Cancer spread

There are 2 stages of cancer spread (Metastasis).

  • M0 means the cancer has not spread to other organs; and
  • M1 means the cancer has spread to other parts of the body.

Your doctor puts the T, N and M results together to give you your stage. For example, you may see a bowel cancer described as T2, N0, M0. This means:

  • The tumour has grown into the muscle layer of the bowel wall;
  • There is no evidence of cancer cells in the lymph nodes; and
  • No evidence of spread to other parts of the body.

Stage 1 bowel cancer

The cancer is in the inner lining of the bowel, or has grown through the inner lining of the bowel into the muscle wall, but no further. There is no cancer in the lymph nodes. In TNM staging, this is the same as:

  • T1, N0, M0; or
  • T2, N0, M0.

Stage 2 bowel cancer

This stage is divided into 2a and 2b.

Stage 2a

This means that the cancer has grown into the outer covering of the bowel wall, but there are no cancer cells in the lymph nodes:

  • T3, N0, M0.

Stage 2b

This means that the cancer has grown through the outer covering of the bowel wall and into tissues or organs next to the bowel. There are no cancer cells in the lymph nodes, and the cancer has not spread to another area of the body:

  • T4, N0, M0.

Stage 3 bowel cancer

Stage 3 is divided into 3 stages

Stage 3a

This means that the cancer is still in the inner layer of the bowel wall or has grown into the muscle layer. Between 1 and 3 nearby lymph nodes contain cancer cells:

  • T1, N1, M0; or
  • T2, N1, M0.

Stage 3b

This means that the cancer has grown into the outer lining of the bowel wall or into surrounding body tissues or organs. Between 1 and 3 nearby lymph nodes contain cancer cells:

  • T3, N1, M0; or
  • T4, N1, M0.

Stage 3c

This means that the cancer can be any size and has spread to 4 or more nearby lymph nodes. The cancer has not spread to any other part of the body:

  • any T, N2, M0.

Stage 4 bowel cancer

The 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.

Grading of bowel cancer

As well as the stage of bowel cancer, doctors also consider what the cancer cells look like under the microscope (the grade) when deciding on treatment. The grade tells you how normal or abnormal the cancer cells are.  As a normal cell grows and matures, it becomes more specialised for its role and place in the body. This is called differentiation. A pathologist grades bowel cancer as:

  • Grade 1 (low grade) – the cancer cells are well differentiated, which means they look quite similar to normal cells
  • Grade 2 (moderate grade) – the cancer cells are moderately differentiated, which means the cells look more abnormal
  • Grade 3 (high grade) – the cancer cells are poorly differentiated, which means they look very abnormal

The grade gives doctors an idea of how the cancer is likely to behave. A low grade cancer is likely to be slower growing and less likely to spread than high grade cancers.