Staging Explained
 

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The American Joint Committee on Cancer (AJCC) TNM System
A staging system is a standardized way for the cancer care team to summarize information about how far a cancer has spread. The most common system used to describe the stages of breast cancer is the American Joint Committee on Cancer (AJCC) TNM system. The stage of a breast cancer can be based either on the results of physical exam, biopsy, and imaging tests (called the clinical stage), or on the results of these tests plus the results of surgery (called the pathologic stage). The staging described here is the pathologic stage, which includes the findings after surgery, when the pathologist has looked at the breast mass and lymph nodes. Pathologic staging is likely to be more accurate than clinical staging, as it allows the doctor to get a firsthand impression of the extent of the cancer.
The TNM staging system classifies cancers based on their T, N, and M stages:

• T stands for tumor (its size and how far it has spread within the breast and to nearby organs).
• N stands for spread to lymph nodes (bean-shaped collections of immune system cells that help fight infections and cancers).
• M is for metastasis (spread to distant organs).

Additional letters or numbers appear after T, N, and M to provide more details about the tumor, lymph nodes, and metastasis:

• The letter T followed by a number from 0 to 4 describes the tumor's size and spread to the skin or to the chest wall under the breast. Higher T numbers indicate a larger tumor and/or wider spread to tissues near the breast.
• The letter N followed by a number from 0 to 3 indicates whether the cancer has spread to lymph nodes near the breast and, if so, how many lymph nodes are affected.
• The letter M followed by a 0 or 1 indicates whether the cancer has spread to distant organs -- for example, the lungs or bones.

Breast Cancer T, N, and M Categories
Primary tumor (T):

TX: Primary tumor cannot be assessed.
T0: No evidence of primary tumor.
Tis: Carcinoma in situ (DCIS, LCIS, or Paget disease of the nipple with no associated tumor mass)
T1: Tumor is 2 cm (3/4 of an inch) or less across.
T2: Tumor is more than 2 cm but not more than 5 cm (2 inches) across.
T3: Tumor is more than 5 cm across.
T4: Tumor of any size growing into the chest wall or skin. This includes inflammatory breast cancer.


Nearby lymph nodes (N) (based on looking at them under a microscope):

NX: Nearby lymph nodes cannot be assessed (for example, removed previously).
N0: Cancer has not spread to nearby lymph nodes.
N1: Cancer has spread to 1 to 3 axillary (underarm) lymph node(s), and/or tiny amounts of cancer are found in internal mammary lymph nodes (those near the breast bone) on sentinel lymph node biopsy.
N2: Cancer has spread to 4 to 9 axillary lymph nodes under the arm, or cancer has enlarged the internal mammary lymph nodes.
N3: 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 involves 4 or more axillary lymph nodes, and tiny amounts of cancer are found in internal mammary lymph nodes on sentinel lymph node biopsy.

Metastasis (M):

MX: Presence of distant spread (metastasis) cannot be assessed.
M0: No distant spread.
M1: Spread to distant organs is present.


Breast Cancer Stage Grouping

Once the T, N, and M categories have been determined, this information is combined in a process called stage grouping. Cancers with similar stages tend to have a similar outlook and thus are often treated in a similar way. Stage is expressed in Roman numerals from stage I (the least advanced stage) to stage IV (the most advanced stage). Non-invasive cancer is listed as stage 0.

Stage 0: Tis, N0, M0: This is ductal carcinoma in situ (DCIS), the earliest form of breast cancer. In DCIS, cancer cells are still within a duct and have not invaded deeper into the surrounding fatty breast tissue. Lobular carcinoma in situ (LCIS) is sometimes classified as stage 0 breast cancer, but most oncologists believe it is not a true breast cancer. In LCIS, abnormal cells grow within the lobules or milk-producing glands, but they do not penetrate through the wall of these lobules. Paget disease of the nipple (without an underlying tumor mass) is also stage 0. In all cases the cancer has not spread to lymph nodes or distant sites.

Stage I: T1, N0, M0: 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 IIA: T0, N1, M0 / T1, N1, M0 / T2, N0, M0: One of the following applies:

• The tumor is 2 cm or less across (or is not found) and has spread to 1 to 3 axillary lymph nodes.
• 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), has spread to 1 to 3 axillary lymph nodes, and tiny amounts of cancer are found in internal mammary lymph nodes 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.

In all cases, the cancer hasn't spread to distant sites.

Stage IIB: T2, N1, M0 / T3, N0, M0: One of the following applies:

• The tumor is larger than 2 cm and less than 5 cm across. It has spread to 1 to 3 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.

The cancer hasn't spread to distant sites.

Stage IIIA: T0-2, N2, M0 / T3, N1-2, M0: One of the following applies:

• The tumor is not more than 5 cm across (or cannot be found). It has spread to 4 to 9 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 1 to 9 axillary nodes, or to internal mammary nodes.

In all cases, the cancer hasn't spread to distant sites.

Stage IIIB: T4, N0-2, M0: The tumor has grown into the chest wall or skin, and one of the following applies:

• It has not spread to the lymph nodes.
• It has spread to 1 to 3 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 4 to 9 axillary lymph nodes, or it has enlarged the internal mammary lymph nodes.

The cancer hasn't spread to distant sites.
Inflammatory breast cancer is classified as stage IIIB unless it has spread to distant lymph nodes or organs, in which case it would be stage IV.

Stage IIIC: T0-4, N3, M0: The tumor is any size (or can't be found), 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 involves 4 or more axillary lymph nodes, and tiny amounts of cancer are found in internal mammary lymph nodes on sentinel lymph node biopsy.

The cancer hasn't spread to distant sites.

Stage IV: T0-4, N0-3, M1: The cancer can be any size and may or may not have spread to nearby lymph nodes. It has spread to distant organs (the most common sites are the bone, liver, brain, or lung), or to lymph nodes far from the breast.

If you have any questions about the stage of your cancer and what it might mean in your case, be sure to ask your doctor.