Stages of breast cancer

Following your diagnosis, testing will be done to determine the stage or extent of your breast cancer. This involves finding out how large the tumor is and whether the cancer is limited to the breast or has spread to other parts of the body.

Breast cancer staging takes into account the size and location of the primary breast tumor, any regional lymph node involvement near the breast and underarm, and any metastatic disease. Based on this information, breast cancers are classified into one of five main stages. The term "early breast cancer" refers to stages of breast cancer labeled 0, I, II, and IIIA. The term "advanced breast cancer" refers to breast cancer stages IIIB and IV.

Knowing the stage of your cancer will help you and your doctor decide on the best course of treatment for you.

Early breast cancer

In stage 0, cancer cells are present in either the lining of a breast lobule or a duct but have not spread to the surrounding fatty tissue. This stage is also called ductal carcinoma in situ (DCIS).

In stage I, cancer has spread from the lobules or ducts to nearby tissue in the breast. At this stage and beyond, breast cancer is considered to be invasive. The tumor is 2 cm or less in diameter (approximately 1 inch or less); the cancer has not spread to the lymph nodes.

In stage II, the tumor can range from 2 cm to less than 5 cm in diameter (approximately 1 to 2 inches); sometimes the cancer may have spread to the lymph nodes.

In stage IIIA, the tumor is 5 cm or greater in diameter (approximately 2 inches or greater) and the cancer has spread into the lymph nodes; or the tumor may be of any size where cancer cells have grown extensively into axillary (underarm) lymph nodes.

Advanced breast cancer

In stage IIIB, known as locally advanced cancer, the tumor may be of any size, but has spread into the skin of the breast or tissues of the chest wall. The cancer may or may not have spread to the lymph nodes.

In stage IV, known as metastatic cancer, the disease has spread from the breast to other parts of the body, such as bone, liver, lung, or brain.

For more information about metastatic breast cancer and how it is treated, see Treatment of advanced breast cancer.