The stages of breast cancer are defined by the size of the tumour and whether or not the cancer has spread or “metastasized”. The stage is determined through testing done on the tumour and lymph nodes after they are removed or during imaging tests performed prior to surgery. You can learn more about each stage below.

Stage 0
In stage 0, also called carcinoma in situ, the cancerous cells are confined to the ducts, lobes or nipple. No cancerous cells are present in the fatty tissue or the lymph nodes. This stage is also sometimes referred to as “pre-cancer”.

Stage IA
In stage IA, the cancer has formed a tumor that is 2 centimetres or less in size. The cancer has not spread outside of the breast.

Stage IB
In stage IB, small clusters of breast cancer cells are found in the lymph nodes. In some cases, there is a small tumor. In other cases, there is no tumor in the breast.

Stage IIA
There are two different kinds of cases that may be classified as stage IIA. In one case, there is no tumour in the breast or the tumor is 2 centimetres or less in size, as it is in stage IA, but cancerous cells have been found in at least 1, but not more than three of the lymph nodes. In the other case, the tumor is between 2 and 5 centimetres in size, but the cancer has not spread to the lymph nodes.

Stage IIB
IIB of the breast cancer stages is used when the tumour is between 2 and 5 centimetres in size and it has spread to the lymph nodes, although only small clusters of cancerous cells, less than 2 millimetres in size are found in the lymph nodes. This classification is also used for tumours larger than 5 centimetres when the cancer has not spread to the lymph nodes.

Stage IIIA
This is one of the breast cancer stages in which cancerous cells are found in the lymph nodes. The tumour may be of any size. When the lymph nodes are involved, there is a greater risk that the cancer will metastasize or spread to other parts of the body.

Stage IIIB
In this stage, the lymph nodes are usually involved and the cancer has spread to the chest wall and/or to the skin to cause an ulcer. If the skin is involved, it may be inflammatory breast cancer, a type in which the entire breast is painful, red and enlarged.

Stage IIIC
In this stage, the cancer has spread even further, often involving the lymph nodes above or below the collarbone, as well as those under the arm and near the breastbone. The skin or chest wall may also be involved. Some stage IIIC cancers are inoperable, while others can still be treated with surgery.

Stage IV
In stage IV, the cancer has spread to other parts of the body via the lymph nodes and the bloodstream. The brain, lungs, liver and bones are most often affected. The prognosis is very poor for this stage.

What you should remember about these breast cancer stages is that any stage can progress to stage IV without treatment. This is why early detection and early treatment is so important.