Staging is used to classify breast cancer and is important in determining what treatment option is best for the patient. The stage of cancer is determined by looking at information from many different tests and studies. The factors that are considered when staging are the size of the primary tumor, lymph node involvement, and the spread of cancer or distant metastasis. The physician will need to take information from each of these factors to determine the stage of the cancer. Listed below are the various stages of cancer with a brief description followed by some more information on the factors that would place a cancer in each stage.

The breast is made up of lobules (milk producing glands), ducts (tubes linking the lobules to the nipple), fatty tissue (the tissue surrounding the lobules and ducts), blood vessels and lymph vessels (similar to blood vessels but carry lymph fluid to lymph nodes under the arm, near the collarbone, and in the chest).

Stage 0 - Considered an early stage breast cancer, has cancer cells in the lining of the lobules or ducts and have not spread beyond into the fatty tissue or beyond the breast.

Stage I - Considered an early stage breast cancer, this cancer has spread from the ducts or lobules into the nearby tissue. The tumor measures 2 centimeters (about 1/4 inch) or smaller in diameter and has not spread beyond the breast.

Stage II - Considered an early stage breast cancer, has spread from the ducts or lobules into the nearby tissue, the tumor measures larger than 2 centimeters (about 1/4 inch), but is not lager than 5 centimeters. The cancer may or may not have spread to the lymph nodes on the same side as the breast cancer.

Stage III - Considered to be in the advanced stages, also known as locally advanced cancer, has subcategories.

Stage IIIa - a tumor measuring more than 5 centimeters (over 2 inches) in diameter and may or may not have spread to the lymph nodes. Stage IIIb - a tumor of any size, which has spread to the skin, chest wall or internal mammary lymph nodes.

Stage IV - Considered to be in the advanced stages, also known as metastatic. This cancer, regardless of size has spread (metasized) to distant sites such bones, liver, lungs or brain, or to lymph nodes not near the breast.