Breast cancer staging

Every breast cancer diagnosis is given a stage and a grade. These, along with the type of cancer, help to determine what treatment is best.

Breast cancer stage refers to how big the cancer is and whether it has spread.

• Stage 0 / ductal carcinoma in situ (DICS) – this is a pre-invasive cancer, meaning there are cancer cells in the breast ducts, but they haven’t spread to the breast tissue. This is 100% survivable with treatment and may never progress to invasive breast cancer.
  
  
• Stage 1 – the earliest invasive breast cancer with only small tumours. This means the cancer is now in the breast tissue. It is considered easy to treat.
  
  
• Stage 2 – Still considered early, but it is either a large tumour or has spread to lymph nodes. Stage 1 and 2 breast cancers have a 92% survival rate at 10 years.
  
  
• Stage 3 - The tumour is larger than stage 2 or it involves the skin of the breast or the chest wall. It might have spread from the breast to more than just a few lymph nodes. Stage 3 has an 82% survival rate at 10 years.
  
  
• Stage 4 -This is referred to as advanced, metastatic or incurable breast cancer. The cancer cells have spread to other parts of the body.

Breast cancer grade refers to what the tumour looks like in comparison with normal cells, which helps determine how quickly the cancer is growing and how it might behave.

Low grade– Usually slow-growing, the cancer cells and structures look more like normal breast cells

Medium grade – Intermediate growth rate, the cancer has fewer features of normal breast tissue

High grade – fast-growing the cancer cells which look very different from normal breast cells

The health system uses the TNM system below to determine breast cancer grade and stage. You might hear some of the following terms or descriptions from your medical team. 

These factors are:

• T - the size of the tumour
• N - the number and location of cancerous lymph nodes
• M - the presence or absence of metastases (secondary cancer spread from the original primary site).

T refers to tumour size

Size is measured under a microscope. It is important because the smaller the tumour, the less likely it is to have spread beyond the breast and the better the chance for successful treatment. Small tumours are generally classified as two centimetres (20mm) or less.

N refers to lymph node status

Lymph node status is determined by a pathologist who examines any nodes under a microscope after they have been removed from the armpit (axilla) during surgery. If any nodes contain cancer cells, they are called positive nodes.

M refers to metastasis

Metastasis is the spread of cancer to other areas of the body, otherwise known as distant spread. Some breast cancer cells have the ability to invade lymphatic and/or blood vessels where they can circulate to distant organs and tissues e.g. bones, liver, lungs and brain. Imaging such as CT scans and bone scans can be performed if the tumour is high risk and/or metastases are suspected.

Until recently breast cancer staging used only these measures to classify the stage of the cancer but in January 2018 the system was updated to take into account additional tumour biology factors that can affect outcomes.

These are:

• tumour grade
• hormone receptor expression
• HER2 over-expression
• the results of genomic tests (if used).

Using this updated system, the extra information provided by these biologic factors may modify the stage that would have been assigned by using anatomic factors alone. For instance a small but high-grade (grade 3) tumour that is hormone receptor positive and HER2 negative would be assessed as one stage higher than previously. Similarly a tumour that is triple negative, regardless of grade, would be determined to be one stage higher, or a larger tumour with a good biologic profile might be downstaged.

Results from predictive genomic panels such as Oncotype Dx may in some cases downgrade tumours by one stage compared to the old system using TNM alone if the results show a low score for risk of recurrence.

The TNM scale ranges from stage 0 to stage IV. A higher stage indicates more advanced cancer. The chart below gives a summary of TNM staging.

Stage should not be confused with Grade (1, 2 or 3), which reflects what the cancer cells look like under a microscope, how different they look from normal healthy breast cells and how actively they are dividing and growing.

Examples of Revisions to Breast Cancer Staging Using Biomarkers and Oncotype DX

Abbreviations:

• −, negative
• O+, positive
• ER, estrogen receptor
• G, grade
• HER2, human epidermal growth factor receptor 2
• M, metastasis classification
• N, lymph node classification
• PR, progesterone receptor
• T, tumor classification
  

Taken from the American Joint Committee on Cancer 2017 (8th edition)