Breast Cancer Staging

If you are diagnosed with breast cancer, your doctor will do tests to determine the stage of your cancer. The stages range from 0 to IV and indicate the extent of the cancer, including its size and if and how far it has spread.

These diagnostic tests can include:

  • Blood tests
  • Bone scans
  • CT scans
  • Mammograms
  • PET scans

Staging is a way to make sure you get the best possible treatment. For most cancers, the stage is based on three main factors:

  • Size of the tumor and whether or not it has grown into nearby areas (T)
  • If the cancer has spread to nearby lymph nodes (N)
  • If the cancer has spread to distant areas of the body (M)

Once the TNM are determined, a stage is assigned to the breast cancer. 

Stage 0

Stage 0 means the cancer cells are still within a duct and have not invaded deeper into the surrounding fatty breast tissue. This is called ductal carcinoma in situ (DCIS), a non-invasive breast cancer.

In stage 0 cancer, the cancer has not spread to lymph nodes or distant sites.

Stage 1

The tumor is 2 cm (about 3/4 of an inch) or less across and has not spread to lymph nodes or distant sites.

Stage IB

The tumor is 2 cm or less across (or is not found) with micrometastases in one to three axillary lymph nodes (the cancer in the lymph nodes is greater than 0.2mm across and/or more than 200 cells but is not larger than 2 mm). The cancer has not spread to distant sites.

Stage IIA

One of the following applies and the cancer hasn't spread to distant sites:

  • The tumor is 2 cm or less across (or is not found) and has spread to one to three axillary lymph nodes, with the cancer in the lymph nodes larger than 2 mm across.
  • The tumor is 2 cm or less across (or is not found) and tiny amounts of cancer are found in internal mammary lymph nodes on sentinel lymph node biopsy.
  • The tumor is 2 cm or less across (or is not found) and has spread to one to three lymph nodes under the arm and to internal mammary lymph nodes (found on sentinel lymph node biopsy).
  • The tumor is larger than 2 cm across and less than 5 cm but hasn't spread to the lymph nodes.

Stage IIB

One of the following applies and the cancer hasn't spread to distant sites:

  • The tumor is larger than 2 cm and less than 5 cm across. It has spread to one to three axillary lymph nodes and/or tiny amounts of cancer are found in internal mammary lymph nodes on sentinel lymph node biopsy.
  • The tumor is larger than 5 cm across but does not grow into the chest wall or skin and has not spread to lymph nodes.

Stage IIIA

One of the following applies and the cancer hasn't spread to distant sites:

  • The tumor is not more than 5 cm across (or cannot be found). It has spread to four to nine axillary lymph nodes, or it has enlarged the internal mammary lymph nodes.
  • The tumor is larger than 5 cm across but does not grow into the chest wall or skin. It has spread to one to nine axillary nodes, or to internal mammary nodes.

Stage IIIB

The tumor has grown into the chest wall or skin but hasn't spread to distant sites, and one of the following applies:

  • It has not spread to the lymph nodes.
  • It has spread to one to three axillary lymph nodes and/or tiny amounts of cancer are found in internal mammary lymph nodes on sentinel lymph node biopsy.
  • It has spread to four to nine axillary lymph nodes, or it has enlarged the internal mammary lymph nodes.

Stage IIIC

The tumor is any size (or can't be found), hasn't spread to distant sites and one of the following applies:

  • Cancer has spread to 10 or more axillary lymph nodes.
  • Cancer has spread to the lymph nodes under the clavicle (collar bone).
  • Cancer has spread to the lymph nodes above the clavicle.
  • Cancer involves axillary lymph nodes and has enlarged the internal mammary lymph nodes.
  • Cancer has spread to four or more axillary lymph nodes, and tiny amounts of cancer are found in internal mammary lymph nodes on sentinel lymph node biopsy.

Stage IV

The cancer can be any size and may or may not have spread to nearby lymph nodes. It has spread to distant organs or to lymph nodes far from the breast. The most common sites of spread are the bone, liver, brain or lung.