If a woman has an abnormal mammography or breast exam, it is appropriate to do a workup to determine whether cancer cells are present. If cancer cells are already present, it must also be determined how much cancer is present and how far the cancerous cells have spread.

The size and spread of the cancer is classified as the stage of the cancer. Knowing the stage of the cancer is important because it is the primary factor in the selection of treatment and in the prognosis for the woman.

Thus, after an abnormal mammography or breast exam, the woman will typically be referred for additional breast imaging with diagnostic mammography, ultrasound, or other imaging tests. Depending on the results of these imaging tests, it may also be appropriate for the physician to order a breast biopsy. The biopsy is the only definitive way to determine whether cancer is present.

The cancer's stage is documented by using a standard system which assigns letters and numbers to indicate the size and spread of the cancer:

The TNM staging system is based on a classification of the size and spread of the Tumor, the involvement of lymph nodes, and metastasis to other organs or to the skeletal system.

T stands for tumor (its size and how far it has spread within the breast and to nearby organs).

TX: Primary tumor cannot be assessed
T0: No evidence of primary tumor (this sometimes happens)
Tis: Carcinoma in situ; intraductal carcinoma, lobular carcinoma in situ, or Paget's disease of the nipple with no associated tumor mass
T1: Tumor 2 cm (4/5 of an inch) or less in greatest dimension
T2: Tumor more than 2 cm but not more than 5 cm (2 inches) in greatest dimension
T3: Tumor more than 5 cm in greatest dimension
T4: Tumor of any size growing into the chest wall or skin

N stands for spread to the regional (nearby) lymph nodes.

NX: Regional lymph nodes cannot be assessed (for example, removed previously)
N0: Cancer has not spread to regional lymph nodes.
N1: Cancer has spread to 1-3 axillary lymph node(s) on the same side as the breast cancer and/or in internal mammary nodes with microscopic disease found by sentinel node biopsy but not found on imaging studies or by clinical exam. This category includes the situation where only a small cluster of cancer cells is detected.
N2: Cancer has spread to 4-9 lymph nodes on the same side as the breast cancer or in internal mammary nodes found by imaging studies or clinical exam in the absence of axillary lymph node metastasis
N3: Cancer has spread to 10 or more axillary lymph nodes, or in infraclavicular (below the collar bone) lymph nodes, or in supraclavicular nodes (above the collar bone) or in internal mammary lymph nodes(located beneath the breast and inside the chest) found by imaging tests or clinical exam in the presence of one or more positive axillary lymph nodes, or in more than 3 axillary lymph nodes and in internal mammary nodes found by sentinel node biopsy but not found by imaging tests or clinical exam - all on the same side as the breast

M stands for whether there is metastasis (spread to distant organs).

MX: Presence of distant spread (metastasis) cannot be assessed
M0: No distant spread
M1: Distant spread is present

The stages are commonly expressed numerically:

• Stage 0 or carcinoma in situ (TISN0M0)

  Ductal carcinoma in situ (DCIS) is the earliest form of breast cancer. In DCIS, cancer cells are located within a duct and have not invaded the surrounding fatty breast tissue. Lobular carcinoma in situ (LCIS), also called lobular neoplasia, is sometimes classified as stage 0 breast cancer, although many oncologists believe it is not a true form of 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.

• Stage I (T1N0M0)

  The tumor is 2 cm (about 4/5 of an inch) or less in diameter and has not spread to lymph nodes or anywhere else.

• Stage II (T0N1M0 T1N1M0, T2N0,N1M0, T3N0M0)

  The tumor is larger than 2 cm in diameter but not larger than 5 cm (2 inches), or it has spread to 1-3 axillary (underarm) lymph nodes on the same side as the breast cancer. Both of these can be present also. The tumor may also be larger than 5 cm but has not spread to lymph nodes.

• Stage III (T0N2M0, T1N2M0, T2N2M0, T3,N2M0, T4AnyN,M0, AnyT,N3,M0)

  The tumor is smaller than 5 cm in diameter and has spread to 4-9 axillary lymph nodes, or the tumor is larger than 5 cm and has spread to 1-9 axillary nodes or the tumor grown into the chest wall or skin and 0-9 nodes are involved, or the tumor is any size has spread to 10 or more nodes in the axilla or to lymph nodes under the clavicle (infraclavicular) or above the clavicle (supraclavicular) or to lymph nodes in the chest near the breast bone (internal mammary).

  Patients with stage III cancer show no signs that the cancer has spread to distant organs or bones.

  Inflammatory breast cancer is classified as stage III, unless it has spread to distant organs or lymph nodes that are not near the breast, in which case it would be stage IV.

• Stage IV (AnyTAnyNM1)

  The cancer, regardless of its size, has metastasized to distant organs such as bones or lungs or to lymph nodes not near the breast.

Once the diagnostic workup is completed, a proper treatment plan can be developed.