What are breast cancer stages?

When an individual is diagnosed with breast cancer, healthcare providers will try to determine if the cancer has spread and, if so, to what extent. This process, known as staging, helps determine how severe the disease is and what the best treatment options are.

To understand breast cancer stages, it helps to understand a little about the tissue that lies beneath the skin. Breast tissue contains around 18 or so lobes, which are made up of smaller structures called lobules. These structures are linked together by tiny tubes called ducts. If you were to look at these structures, they might remind you of a very small cluster of grapes or small trees with rounded leaves. These structures make it easy for a tumor to grow into another area of the breast.

Each breast also has vessels that carry lymph or blood throughout the body. Lymph is a thin, clear fluid that circulates throughout the body to remove waste, bacteria and other substances from tissues. There are hundreds of lymph nodes in the body, with large clusters of them near the breast, under the arm and above the collarbone. If cells from a cancerous tumor are picked up by either the lymph or blood, it can travel to another part of the body and start growing another tumor.

The system most often used for staging breast tumors is the American Joint Committee on Cancer (AJCC) and International Union for Cancer Control (UICC) TNM system, which is based on seven key pieces of information:

• T: The extent and size of the tumor
• N: The number of lymph nodes affected
• M: Signs indicating if the cancer has metastasized (spread) to other organs
• ER status: If the tumor has estrogen receptors
• PR status: If the tumor has progesterone receptors
• HER2 status: If the cancer makes too much of a protein called HER2
• G: The grade of the tumor or how much the cancer cells look like normal cells

Numbers or letters after T, N and M provide more details about each of these factors, with higher numbers meaning that the cancer is more advanced. The TNM numbers are based on a biopsy, where a small piece of the mass is removed and examined. This is done either in surgery or in an office where a small needle is introduced through the skin into the suspected tumor. If it is a tumor, providers combine this information with information from the physical exam and imaging, such as ultrasounds, computerized tomography (CT) and magnetic resonance imaging (MRI), to assign an overall cancer stage. Or you may have surgery to visualize the mass and see if it has spread. In general, staging based on biopsies is more accurate than staging based on blood tests.

Breast cancer is staged in five levels, 0 through 4, and may be subdivided using letters such as A and B.  The lower the number, the less the cancer has spread.

• Stage 0 breast cancer indicates a cancer that has not extended to other tissues.
• Stage I (1) breast cancer, stage II (2) breast cancer and stage III (3) breast cancer indicate cancers that have grown into the connective tissue or the skin of the breast. The cancer may have spread to nearby tissue, but it is not thought to have spread outside of the breast.
• Stage IV (4) breast cancer is a stage where another cancer, not in the breast, is present at diagnosis. It is also called Stage IV (4) metastatic breast cancer.

• Over 4 million women were estimated to be living in the United States with a history of invasive breast cancer
• Around another 300,000 women are expected to be newly diagnosed in 2022
• More than 150,000 women breast cancer survivors are living with metastatic disease, three-fourths of whom were originally diagnosed with stage I, II or III cancer
• An estimated 2,710 men in the United States will be diagnosed with breast cancer in 2022

People often wonder about survival rates for different stages of breast cancer. The five-year survival rate tells you how many people out of 100 who are diagnosed will live at least five years after the cancer is found. However, it is difficult to accurately estimate an individual’s chances of survival because these statistics are averages. Each person’s chance of recovery can depend on many factors, including:

• Age
• Underlying health conditions
• The size of the tumor, the number of lymph nodes involved and other features of the tumor that affect how quickly a tumor will grow and how well it will respond to treatment 

In addition, survival statistics are reported only every five years and the estimates may not reflect the results of advancements in how people with breast cancer are diagnosed or treated from the last five years. Survival rates for both women and men are continuing to improve, largely attributed to advances in early detection and hormonal treatments. Even if the cancer is found at a more advanced stage, new treatments help many people with breast cancer maintain a good quality of life for some time.

Whatever stage of breast cancer you have, work with a healthcare team that’s knowledgeable about the latest treatments. Your healthcare providers should be willing to work with you to make sure you understand your diagnosis, possible treatment options, and help you make informed decisions in your care. Don't be afraid to ask questions, and work closely with your providers to optimize treatment.

Published February 2020. Clinically reviewed and updated by Nancy Kupka, PhD, RN, October 2022.