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Breast Cancer
Staging Breast Cancer
As with other cancers, breast cancer is classified in stages according to the system developed by the American Joint Committee on Cancer (AJCC), which was last updated in 2009. This tumor (T), node (N), and metastasis (M) classification is then used as the foundation for the overall stage of breast cancer. Staging is categorized as clinical or pathologic. Clinical staging, which is done by the managing physician, is based on the characteristics of the tumor as assessed clinically; that is, by physical examination, x-rays and/or other imaging studies, and laboratory results. Pathologic staging is done by a pathologist who examines tissue specimens removed during surgery. Staging categories are defined on the basis of how outcomes differ according to specific characteristics of the tumor, and treatment options vary according to stage.
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 (Table 1, on page 16). Clinical staging for the N category describes what lymph nodes appear to be involved (that is, have evidence of breast cancer cells). The anatomic location of involved lymph nodes is important, as disease is more extensive the farther away the involved nodes are from the breast. The pathologic N category (denoted as pN) provides more specific details, such as how many lymph nodes are involved and the amount of tumor cells actually found in the nodes (Table 2).
M category indicates whether there is evidence of distant metastasis (spread of cancer to another part of the body). Staging for the M category is primarily clinical, 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 (Table 3).
The overall stage of breast cancer ranges from 0 to IV. Stage 0 breast cancer is noninvasive; that is, cancer cells are found only inside the ducts or lobules in the breast (Tis). A breast cancer that is small (T1) is classified as stage I disease. The updated AJCC staging system now subclassifies stage I disease as either stage IA or stage IB. With stage IA breast cancer, there is no spread of disease to lymph nodes (pN0), and with stage IB breast cancer, there is micrometastasis in the nodes (pN1mi). Micrometastasis refers to a very limited number of tumor cells in a node.
Stage II breast cancer is also subclassified as either stage IIA or IIB. Stage IIA breast cancer describes one of several situations. The tumor may be small (T1) with spread to the axillary lymph nodes (pN1), the tumor may be larger (T2) but with no spread to the lymph nodes (pN0), or there may be no evidence of a tumor in the breast (T0) but there are cancer cells in the axillary lymph nodes (pN1). Stage 0, I, or IIA represent early stage breast cancer.
Later stage disease is defined as stage IIB and stage III disease. Stage IIB describes a medium-size tumor (T2) that has spread to no more than three axillary lymph nodes (pN1). Stage IIB also indicates a large tumor (T3) that has not spread to lymph nodes (pN0).
Stage III breast cancer is subclassified as stage IIIA, IIIB, or IIIC. Stage IIIA breast cancer is defined as a tumor that is either smaller than 5 cm (T1 or T2) and has spread to the axillary lymph nodes (N2) or that is larger than 5 cm (T3) and has spread to nearby lymph nodes (pN1 or pN2). Stage IIIB breast cancer includes locally advanced tumors in the breast with extension to the chest wall, swelling, ulceration and inflammatory carcinoma (T4), that may or may not have spread to nearby lymph nodes (pN0, pN1 or pN2). Stage IIIC is characterized by extensive spread to lymph nodes (pN3); the tumor can be of any size and extension (any T).
Stage IV breast cancer is considered to be advanced disease, and the characteristic of this stage is metastasis (any T, any N, M1). Breast cancer usually spreads first to the bone, the lungs, or the liver.
Clinical and/or pathologic staging is an essential component in diagnosing a specific breast cancer, along with testing for estrogen and progesterone receptors and human epidermal growth factor receptor-2 (HER2). The managing physician considers the stage and these other factors in selecting the most appropriate treatment choices, including options for chemotherapy agents, targeted therapies, and hormone treatments (Table 4).
Table 1. American Joint Committee on Cancer System (AJCC) for Classifying a Breast Cancer Tumor (T)
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T Category |
Size of Tumor |
Description of Subcategories |
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Tx |
Cannot be assessed |
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T0 |
No tumor is evident |
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Tis |
Tumor has not started growing into the breast tissue (known as carcinoma in situ) |
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T1 |
2 cm (about 3/4 inch) or less |
T1mi: 1 mm or less
T1a: larger than 1 mm but not more than 5 mm (0.5 cm)
T1b: larger than 5 mm but not more than 10 mm (1 cm)
T1c: larger than 10 mm but not more than 2 cm
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T2 |
larger than 2 cm but not more than 5 cm (almost 2 inches) |
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T3 |
larger than 5 cm |
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T4 |
Any size |
T4a: tumor extends into the chest wall
T4b: presence of edema (swelling), thickening of the skin, or ulceration (a sore, painful area where the breast skin/tissue is breaking down)
T4c: signs of both T4a and T4b
T4d: inflammatory cancer (the breast is red, swollen, and warm)
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Table 2. American Joint Committee on Cancer System (AJCC) for Classifying Breast Cancer Spread to Lymph Nodes (N)
pN Category
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Location and Number of Lymph Nodes with Metastasis or Micrometastases*
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pNx |
Cannot be evaluated or found |
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pN0 |
No metastasis or micrometastases found in any lymph nodes |
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pN1
pN1mi
pN1a
pN1b
pN1c
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Micrometastases
Metastasis in 1-3 axillary lymph nodes (nodes under the arm), with at least one metastasis of more than 2 mm (0.5 cm)
Metastasis in internal mammary lymph nodes (nodes on either side of the sternum [breastbone])
Metastasis in 1-3 axillary lymph nodes and in internal mammary lymph nodes
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pN2
pN2a
pN2b
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Metastasis in 4-9 axillary lymph nodes
Metastasis in internal mammary lymph nodes, but no metastasis in axillary lymph nodes
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pN3
pN3a
pN3b
pN3c
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Metastasis in 10 or more axillary lymph nodes OR in the infraclavicular lymph nodes (nodes under the clavicle [collarbone])
Metastasis in internal mammary lymph nodes and in 1 or more axillary lymph nodes
Metastasis in supraclavicular lymph nodes (nodes above the clavicle)
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*Micrometastases refers to a small cluster of tumor cells, no larger than 2 millimeters.
Table 3. American Joint Committee on Cancer System (AJCC) for Classifying Breast Cancer Metastasis (M)
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M Category |
Description |
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M0 |
No distant metastasis |
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M0(i+) |
Microscopic or molecular evidence of tumor cells in bone marrow or less circulating tumor cells in tissues other than lymph nodes (but no clinical evidence of metastasis) |
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M1 |
Evidence of distant metastasis |
Additional Sources of Information
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