After breast cancer has been diagnosed, tests are done to find out if cancer cells have spread within the breast or to other parts of the body.

The process used to find out whether the cancer has spread within the breast or to other parts of the body is called staging. The information gathered from the staging process determines the stage of the disease. It is important to know the stage in order to plan treatment. The following tests and procedures may be used in the staging process:

• Chest x-ray: An x-ray of the organs and bones inside the chest. An x-ray is a type of energy beam that can go through the body and onto film, making a picture of areas inside the body.
• CT scan (CAT scan): A procedure that makes a series of detailed pictures of areas inside the body, taken from different angles. The pictures are made by a computer linked to an x-ray machine. A dye may beinjected into a vein or swallowed to help the organs or tissues show up more clearly. This procedure is also called computed tomography, computerized tomography, or computerized axial tomography.
• Bone scan: A procedure to check if there are rapidly dividing cells, such as cancer cells, in the bone. A very small amount of radioactive material is injected into a vein and travels through the bloodstream. The radioactive material collects in the bones and is detected by a scanner.
• PET scan (positron emission tomography scan): A procedure to find malignant tumor cells in the body. A small amount of radioactive glucose (sugar) is injected into a vein. The PET scanner rotates around the body and makes a picture of where glucose is being used in the body. Malignant tumor cells show up brighter in the picture because they are more active and take up more glucose than normal cells do.

There are three ways that cancer spreads in the body.

The three ways that cancer spreads in the body are:

• Through tissue. Cancer invades the surrounding normal tissue.
• Through the lymph system. Cancer invades the lymph system and travels through the lymph vessels to other places in the body.
• Through the blood. Cancer invades the veins and capillaries and travels through the blood to other places in the body.

When cancer cells break away from the primary (original) tumor and travel through the lymph or blood to other places in the body, another (secondary) tumor may form. This process is called metastasis. The secondary (metastatic) tumor is the same type of cancer as the primary tumor. For example, if breast cancer spreads to the bones, the cancer cells in the bones are actually breast cancer cells. The disease is metastatic breast cancer, not bone cancer.

The following stages are used for breast cancer:

Stage 0 (carcinoma in situ)

There are 2 types of breast carcinoma in situ:

• Ductal carcinoma in situ (DCIS) is a noninvasive condition in which abnormal cells are found in the lining of a breast duct. The abnormal cells have not spread outside the duct to other tissues in the breast. In some cases, DCIS may become invasive cancer and spread to other tissues, although it is not known at this time how to predict which lesions will become invasive.
• Lobular carcinoma in situ (LCIS) is a condition in which abnormal cells are found in the lobules of thebreast. This condition seldom becomes invasive cancer; however, having lobular carcinoma in situ in one breast increases the risk of developing breast cancer in either breast.

Stage I

In stage I, cancer has formed. Stage I is divided into stages IA and IB.

• In stage IA, the tumor is 2 centimeters or smaller and has not spread outside the breast.
• In stage IB, either:
• no tumor is found in the breast, but small clusters of cancer cells (larger than 0.2 millimeter but not larger than 2 millimeters) are found in the lymph nodes; or
• the tumor is 2 centimeters or smaller and small clusters of cancer cells (larger than 0.2 millimeter but not larger than 2 millimeters) are found in the lymph nodes.

Stage II

Stage II is divided into stages IIA and IIB.

• In stage IIA:
• no tumor is found in the breast, but cancer is found in the axillary lymph nodes (lymph nodes under the arm); or
• the tumor is 2 centimeters or smaller and has spread to the axillary lymph nodes; or
• the tumor is larger than 2 centimeters but not larger than 5 centimeters and has not spread to the axillary lymph nodes.
• In stage IIB, the tumor is either:
• larger than 2 centimeters but not larger than 5 centimeters and has spread to the axillary lymph nodes; or
• larger than 5 centimeters but has not spread to the axillary lymph nodes.

Stage IIIA

In stage IIIA:

• no tumor is found in the breast. Cancer is found in axillary lymph nodes that are attached to each other or to other structures, or cancer may be found in lymph nodes near the breastbone; or
• the tumor is 2 centimeters or smaller. Cancer has spread to axillary lymph nodes that are attached to each other or to other structures, or cancer may have spread to lymph nodes near the breastbone; or
• the tumor is larger than 2 centimeters but not larger than 5 centimeters. Cancer has spread to axillary lymph nodes that are attached to each other or to other structures, or cancer may have spread to lymph nodes near the breastbone; or
• the tumor is larger than 5 centimeters. Cancer has spread to axillary lymph nodes that may be attached to each other or to other structures, or cancer may have spread to lymph nodes near the breastbone.

Stage IIIB

In stage IIIB, the tumor may be any size and cancer:

• has spread to the chest wall and/or the skin of the breast; and
• may have spread to axillary lymph nodes that may be attached to each other or to other structures, or cancer may have spread to lymph nodes near the breastbone.

Cancer that has spread to the skin of the breast is inflammatory breast cancer. See the section on Inflammatory Breast Cancer for more information.

Stage IIIC

In stage IIIC, there may be no sign of cancer in the breast or the tumor may be any size and may have spread to the chest wall and/or the skin of the breast. Also, cancer:

• has spread to lymph nodes above or below the collarbone; and
• may have spread to axillary lymph nodes or to lymph nodes near the breastbone.

Cancer that has spread to the skin of the breast is inflammatory breast cancer. See the section on Inflammatory Breast Cancer for more information.

Stage IIIC breast cancer is divided into operable and inoperable stage IIIC.

In operable stage IIIC, the cancer:

• is found in ten or more axillary lymph nodes; or
• is found in lymph nodes below the collarbone; or
• is found in axillary lymph nodes and in lymph nodes near the breastbone.

In inoperable stage IIIC breast cancer, the cancer has spread to the lymph nodes above the collarbone.

Stage IV

In stage IV, the cancer has spread to other organs of the body, most often the bones, lungs, liver, or brain.