Breast Cancer


Breast cancer is staged according to how much cancer is in the body and where it is located. Classification and staging describes the extent of the cancer, based on the original tumor and whether or how much it has spread (see Staging Illustrations).

To help plan the best course of treatment, physicians classify breast cancer into Stages 0 through IV using the TNM staging system developed by the American Joint Committee on Cancer (AJCC). AJCC staging is based on the tumor’s characteristics as assessed through a physical exam, X-rays, scans and/or other imaging studies, and laboratory results (see Tables 1 and 2). Stage 0 breast cancer is also referred to as in situ breast cancer or noninvasive breast cancer, and Stage IV represents breast cancer that has spread beyond the breast and nearby nodes and tissues.

The tumor (T) classification is the same for both clinical and pathologic staging. This category provides information on the size and extent of the tumor within the breast.

Clinical staging for the node (N) category describes which lymph nodes have evidence of breast cancer cells. The anatomic location of the involved nodes is important because it shows the extent the disease has spread. The pathologic N (node) category (sometimes denoted as pN) shows how many lymph nodes are involved and the amount of tumor cells actually found in the nodes based on the surgical specimen.

The metastasis (M) category indicates evidence of distant metastasis (spread of cancer to another part of the body beyond the breast and local lymph nodes). Staging for the M category is primarily clinical such as by scans, although a new M subcategory is based on the presence of tumor cells that can be detected only by microscopic examination or with molecular testing. The most common sites of distant metastasis in breast cancer are the bones, lungs, liver and brain.

After the breast cancer has been classified according to this system, an overall stage is assigned. Five stages are subdivided to group tumors with similar prognoses (Table 1). This grouping enables doctors to more accurately predict the outcome according to the stage.

AJCC also recommends testing for estrogen and progesterone receptors (ER and PR) and human epidermal growth factor receptor-2 (HER2). The physician then considers the stage and these other factors in selecting the most appropriate treatment choices.

Table 1. Stages of Breast Cancer

Stage TNM Classification
0 Tis, N0, M0
IA T1*, N0, M0
IB T0 or T1*, N1mi, M0
IIA T0 or T1*, N1**, M0
T2, N0, M0
IIB T2, N1, M0
T3, N0, M0
IIIA T0-T3, N2, M0
T3, N1, M0
IIIB T4, N0-N2, M0
IIIC Any T, N3, M0
IV Any T, Any N, M1

*T1 includes T1mi.

**T0 and T1 tumors with micrometastases in node(s) only are excluded from Stage IIA and are classified Stage IB.

Table 2. TNM System for Classifying Breast Cancers

Category Definition
Tumor (T)
Tx The tumor cannot be assessed.
T0 No evidence of primary tumor.
Tis Known as carcinoma in situ; the tumor has not started growing into the breast tissue.
Tumor is 2 centimeters (cm) (about ¾ inch) or less.
Tumor is 1 millimeter (mm) or less.
Tumor is larger than 1 mm but not more than 5 mm (0.5 cm).
Tumor is larger than 5 mm but not more than 10 mm (1 cm).
Tumor is larger than 10 mm but not more than 2 cm.
T2 Tumor is larger than 2 cm but not more than 5 cm (almost 2 inches).
T3 Tumor is larger than 5 cm.

Tumor may be any size but has grown into the chest wall and/or into the skin.
Tumor extends into the chest wall.
The skin shows the presence of one or more of the following: edema (swelling), ulceration (a sore, painful area where the breast skin/tissue is breaking down), or satellite skin nodules (an additional tumor cell mass) in the same breast.
Signs of both T4a and T4b are present.
Breast is red, swollen and warm, indicating inflammatory carcinoma.
Node (N)
Nx Lymph nodes cannot be evaluated.
N0 No metastasis or micrometastasis* (less than or equal to 0.2 mm) found in any lymph nodes.

Micrometastases* are found in lymph nodes (more than 0.2 mm up to 2 mm).
Cancer cells have spread to 1 to 3 axillary lymph nodes (nodes under the arm), with at least one metastasis of more than 2 mm (0.2 cm).
Cancer cells have spread to internal mammary lymph nodes (nodes on either side of the sternum [breastbone]), not detected by physical exam or imaging.
Cancer cells have spread to 1 to 3 axillary lymph nodes and to internal mammary lymph nodes.

Cancer cells have spread to 4 to 9 axillary lymph nodes.
Cancer cells have spread to clinically detected internal mammary lymph nodes but not to axillary lymph nodes.



Cancer cells have spread to 10 or more axillary lymph nodes OR to the infraclavicular lymph nodes (nodes under the clavicle [collarbone]).

Cancer cells have spread to clinically detected internal mammary lymph nodes and to 1 or more axillary lymph nodes.

Cancer cells have spread to supraclavicular lymph nodes (nodes above the clavicle).
Metastasis (M)
M0 Cancer has not spread to other parts of the body (beyond the breast and local lymph nodes).
cM0(i+) There is no evidence of cancer spread, but deposits of tumor cells can be detected at the microscopic or molecular level in the blood, bone marrow or other nodal tissue.
M1 There is clinical evidence that cancer has spread to other parts of the body.

*Refers to a small cluster of tumor cells.

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