The stage of a cancer is a measure of how far it has progressed.  So, a breast cancer that is small and confined to the breast is at an early stage, whereas one that has spread to many different parts of the body is at an advanced stage. 

Over the years a number of different staging systems have been suggested for breast cancer.  The two most widely used are probably the TNM and Manchester classifications.

The TNM scheme looks at the primary tumour in the breast (T), the nearby lymph nodes (also known as lymph glands) (N) and whether or not there is spread of the cancer to other parts of the body, metastases (M).

The TNM staging is actually quite complicated but a simplified version is as follows:

For the primary tumour (T):

• Tis - the cancer is an ‘in situ’ non-invasive tumour
• T1 - the largest diameter of the cancer is 2 centimetres or less
• T2 – the largest diameter of the cancer is between 2 to 5 centimetres
• T3 – the largest diameter of the cancer is more than 5 centimetres
• T4 – the tumour is invading into the skin overlying the breast and/or the  muscle beneath the breast

For the lymph nodes (N):

• N0 – there are no signs of tumour spread to the lymph nodes
• N1 – the lymph nodes under the arm are involved

For the metastases (M):

• M0 – there are no signs of spread to other parts of the body
• M1 – spread to other parts of the body has occurred

So, using the TNM scheme, a cancer that was 1 centimetre across, with no signs of spread to the lymph nodes or other parts of the body, would be a T1 N0 M0 tumour. Similarly, a cancer that was 3 centimetres across, with signs of spread to the lymph nodes and, say, the bones, would be a T2 N1 M1 tumour.

The Manchester system is based on a scheme originally worked out at the Christie Hospital in Manchester in the 1940s. Over the years various versions of this have been used and the following is a typical example:

• Stage 1 – the cancer is limited to the breast with no sign of spread
• Stage 2 – there is spread of the tumour to the lymph nodes under the arm
• Stage 3 – the tumour is invading either the skin covering the breast or the muscle beneath the breast (or both)
• Stage 4 – there is spread of the cancer to other parts of the body

No one staging scheme has ever been shown to be clearly better than any other and so different hospitals use different systems.  Although this may sound confusing the various schemes can all be related (so, for example a T1 N0 M0 cancer on the TNM scheme, would be Stage1 on the Manchester scheme, whereas a T2 N1 M1 tumour would be Stage 4). 

Doctors use the results of physical examinations, tests and operation findings to decide the stage of a breast cancer. Sometimes the stage will change as more results become available. For example, someone who might have an examination and mammogram which suggests their tumour is confined to the breast, suggesting it is a Stage I tumour, but when an operation is done, and the nearby lymph nodes are examined under a microscope, small seedlings of tumour may be found in the lymph glands, making it a Stage II.
 
Using a staging system has two main benefits.  Firstly it gives an idea of the size of abreast cancer and whether it has spread at all and also helps predict what the likely outcome of treatment may be. Secondly, ‘staging’ the cancer determines what the treatment should be, since usually the treatment for an early stage breast cancer will be different from that for a more advanced tumour.