Breast Cancer Staging

Breast cancer staging is an important part of your pathology report and helps your healthcare team choose the best treatment for you. Staging shows how much cancer may be in your body and helps predict chances of the cancer coming back (your recurrence risk), how well treatment may work, and your overall outlook (prognosis).

Staging is based on:

• Invasiveness: Has the cancer spread beyond the milk ducts or lobules?
• Tumour size: How big is the cancer?
• Lymph node involvement: Has the cancer spread to nearby lymph nodes?
• Metastasis: Has the cancer spread to other parts of the body?

How is Staging Done?
Staging is determined through imaging tests, biopsies, and lymph node assessment. Not everyone will need every test. In many cases, lymph nodes under the arm (called axillary nodes) are removed and examined under a microscope to check for cancer cells, helping guide treatment decisions.

Common Terms in Breast Cancer Staging

• Local: Cancer is only in the breast and has not spread
• Regional: Cancer has spread to nearby lymph nodes
• Distant: Cancer has spread to other parts of the body (metastatic breast cancer)

TNM Staging System
Breast cancer is staged using the TNM system, which classifies tumours based on:

• Tumour (T): Describes tumour size and extent (T0 = no tumour, T4 = large tumour affecting skin or chest wall)

• Nodes (N): Whether the cancer has spread to the lymph nodes (N0 = no spread, N3 = spread to multiple lymph nodes)
• Metastases (M): Whether the cancer has spread to other parts of the body (M0 = no metastasis, M1 = metastasis present)

Stages range from 0 to IV based on TNM classification, for example:

• T1N0M0: Small tumour, no lymph node involvement or metastases (Stage I)
• T4N3M1: Large tumour, significant lymph node involvement, and distant spread (Stage IV)

Breast Cancer Stages

• Stage 0: Non-invasive cancer (cancer cells remain in their original location)
• Stage I: Small, localized invasive tumour that has not spread to lymph nodes
• Stage II: Larger tumour that may involve nearby lymph nodes
• Stage III: More advanced cancer with significant lymph node involvement
• Stage IV: Metastatic breast cancer (cancer has spread to distant parts of the body)

Metastatic Breast Cancer (Stage IV)
Metastatic breast cancer (also known as advanced or Stage IV breast cancer) means the cancer has spread beyond the breast to other parts of the body. About 5% of people diagnosed with breast cancer each year are first diagnosed at stage IV. Others may be diagnosed with early-stage breast cancer that later spreads. Currently, there is no national data in Canada that tracks how many people progress from early-stage to metastatic breast cancer.

How Does Cancer Spread?
Cancer can spread (metastasize) when cancer cells travel to other parts of the body. This can happen before a person is diagnosed with breast cancer (known as de novo metastatic breast cancer), or it can happen after treatment for early-stage breast cancer (known as recurrence). While breast cancer can spread anywhere, it most commonly affects the bones, lungs, liver, brain, and skin. The area where cancer has spread is called the metastatic site.

Learn More

• Visit our Living with Metastatic Breast Cancer section to better understand your diagnosis. 

• For in-depth guidance, refer to our Metastatic Breast Cancer Handbook: A Guide for Individuals Living With Stage IV Breast Cancer 
• Speak with your healthcare provider if you have questions about staging or your diagnosis

Medical Review by Roochi Arora, MD, FRCPC, August 2025

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