Breast cancer staging
Cancer is staged using the TNM system. This calculates how advanced a cancer is by evaluating anatomic factors that can help determine the likely prognosis and appropriate treatment plan.
T refers to tumour size. Small tumours are less likely to have spread beyond the breast, resulting in better outcomes for treatment. Small tumours are generally classified as 20mm or less. N refers to the lymph node status (the number and location of cancerous lymph nodes). If any contain cancer cells, they are called positive nodes. M refers to the presence or absence of metastases.
Other factors, such as tumour grade, hormone receptor expression, HER2 over-expression and the results of any genomic testing, can also affect cancer staging.
The staging scale ranges from stage O to stage IV, where a higher stage indicates more advanced cancer. The chart below gives a summary of TNM staging:
The TNM staging system for breast cancer
| Stage | Tumour size | Axillary lymph nodes | Metastasis |
| 0 (in situ) | Cluster of cancer cells in a breast duct (in situ) | No spread | None |
| I | Up to 2cm | No spread | None |
| II | Smaller than 2cm | Spread to axillary lymph nodes | None |
| Between 2-5cm | May or may not have spread to axillary lypmh nodes | None | |
| Larger than 5cm | No spread | None | |
| III | Any size | Has spread to multiple axillary lymph ndoes so that the nodes have become attached to each other |
None |
| Larger than 5cm | Has spread to axillary lymph nodes | None | |
| Any size but cells have spread to skin or chest wall | May or may not have spread to axillary lypmh nodes | None | |
| Any size | Has spread to lymph nodes along breastbone and above/below collarbone | None | |
| IV | Any size | May or may not have spread to axillary lypmh nodes | Has spread to other organs of the body or the skin and lymph nodes about the collarbone |
