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Staging is the process of assessing how far the cancer has spread and is important in making treatment decisions and determining prognosis.

The TNM system provides information about three different aspects of the disease:

• T = Tumor

  • followed by a number 0 through 4 (T0; T1; T2; T3; T4)
  • describes the tumor's size and spread to the skin or chest wall under the breast.
  • a higher number means a larger tumor and/or more spread to tissues near the breast

• N = Lymph Nodes

  • followed by a number 0 through 3 (N0; N1; N2; N3)
  • indicates whether the cancer has spread to the lymph nodes near the breast, and if so, whether the affected nodes are attached (fixed) to other structures under the arm

• M = Metastasis

  • followed by a 0 or 1 (M0; M1)
  • indicates whether the cancer has spread (metastasized) to other organs of the body or to lymph nodes that are not next to the breast

The individual TNM scores are combined and are used to classify breast cancer into the following Stages of disease:

• Stage 0 - Noninvasive, Carcinoma in situ

• Stage I - Cancer cells have not spread beyond the breast and the tumor is no more than about 2 centimeters (cm), or about an inch, across

• Stage II - This stage is divided into two groups:

  • Stage IIA

    • the tumor in the breast is less than 2 cm across and the cancer has spread to the lymph nodes under the arm but not to other parts of the body; OR
    • the tumor is less than 5 cm but has not spread to the lymph nodes under the arm or to other parts of the body; OR
    • no tumor is visible in the breast, however, cancer cells have been detected in the lymph nodes under the arm but the cancer has not spread to other parts of the body

  • Stage IIB

    • the tumor is less than 5 cm but the cancer has spread to the lymph nodes under the arm but not to other parts of the body; OR
    • the tumor is large (more than 5 cm across), however, cancer cells have not been detected in the lymph nodes under the arm and there is no spread of the cancer to other parts of the body

• Stage III - "Locally advanced cancer" - This stage is divided into 3 groups:

  • Stage IIIA

    • no tumor is visible in the breast, however, the cancer has spread to the lymph nodes under the arm (which are stuck together) but the cancer has not spread to other parts of the body; OR
    • the tumor is small (5 cm or less) and the cancer has spread to lymph nodes under the armpit (which are stuck together) but the cancer has not spread to other parts of the body; OR
    • the tumor is large (more than 5 cm) and the cancer has spread to lymph nodes under the armpit (which may or may not stuck together) but the cancer has not spread to other parts of the body

  • Stage IIIB