Understanding breast cancer staging

ROCHESTER, Minn. — After breast cancer has been diagnosed, additional tests may help determine if the disease has spread outside the breast. These and other tests contribute to a process called staging. Breast cancer staging helps patients and their doctors develop a treatment strategy and understand the most likely outcome or prognosis.

Although breast cancer staging is a complex classification system that can change as physicians learn more about the disease, it is helpful for patients to understand what factors physicians consider when identifying a diagnosis. A new feature on MayoClinic.com explains the stages of breast cancer and describes one of the most common current staging methods.

The TNM staging system includes three key components:

• Tumor (T). How large is the tumor, and has it spread to the skin or chest wall muscle? Tumor size is one of the most important predictors of how a cancer will behave.
• Node (N). Have cancer cells spread to nearby lymph nodes? Doctors note how many lymph nodes under the arm (axillary lymph nodes) test positive for cancer, because lymph node status strongly relates to prognosis. Breast cancers may be described as "node positive" or "node negative."
• Metastasis (M). Has the cancer spread to other, distant areas of the body?

The numbers assigned in these categories indicate the degree of tumor growth or spread. For example, N0 means no axillary lymph nodes are affected, while N1 means one to three nodes are positive and N2 means four to nine positive nodes.

An interactive slide show on MayoClinic.com shows how the stage of breast cancer, on a scale from stage 0 to stage IV, reflects the cancer's extent.

In addition, MayoClinic.com has recently posted a podcast about inflammatory breast cancer, a particularly rare and aggressive form of cancer.

• Breast cancer staging
• Breast cancer
• Slide show: Stages of breast cancer
• Podcast: Inflammatory breast cancer — Know the symptoms