Understand breast cancer

Breast cancer is the second most common type of cancer in American women.

The information on this page may help you gain a better understanding of your breast cancer diagnosis and what’s happening to your body. This may help when making important decisions with your doctor.

What is breast cancer?

Breast Cancer Starts When Healthy Cells Change and Begin to Grow Out of Control and Turn Into a Tumor

Breast cancer starts when healthy cells change and begin to grow out of control and turn into a tumor. Tumors can begin in different areas of the breast, like the glands that make breast milk, the ducts that carry milk to the nipple, or other tissue regions.

Having a family history of breast cancer, including inherited gene mutations, can increase the risk of developing breast cancer.

Stages of breast cancer

From the National Cancer Institute (NCI)

The information below is based on information originally published by the National Cancer Institute (NCI), the US government’s main agency for cancer research.

The TNM system, the grading system, and biomarker status are combined to find out your breast cancer stage.

TNM system for breast cancer

Breast cancer is categorized with the “TNM” system. TNM looks at the tumor (T), the lymph nodes (N), and if the cancer has spread to other areas in the body (M).

TNM stands for:

  • Tumor (T): The size and location of the tumor
  • Lymph Node (N): The size, location, and number of lymph nodes where cancer has spread
  • Metastasis (M): The spread of the cancer to other parts of the body

Grading system for breast cancer

The grading system describes a tumor based on how abnormal the cancer cells and tissue look under a microscope and how quickly the cancer cells are likely to grow and spread. Three grades are possible:

  • G1
  • G2
  • G3

Biomarker testing for breast cancer

Biomarker testing is used to find out whether breast cancer cells have certain receptors. For breast cancer, biomarker testing includes the following:

  • Estrogen receptor (ER): If the breast cancer cells have estrogen receptors, the cancer cells are called ER positive (ER+). If the breast cancer cells do not have estrogen receptors, the cancer cells are called ER negative (ER-).
  • Progesterone receptor (PR): If the breast cancer cells have progesterone receptors, the cancer cells are called PR positive (PR+). If the breast cancer cells do not have progesterone receptors, the cancer cells are called PR negative (PR-).
  • Human epidermal growth factor type 2 receptor (HER2/neu or HER2): If the breast cancer cells have larger than normal amounts of HER2 receptors on their surface, the cancer cells are called HER2 positive (HER2+). If the breast cancer cells have a normal amount of HER2 on their surface, the cancer cells are called HER2 negative (HER2-). HER2+ breast cancer may grow more quickly and may be more likely to spread to other parts of the body.
  • Triple Positive: If the breast cancer cells do have estrogen receptors, progesterone receptors, and a larger than normal amount of HER2 receptors, the cancer cells are called triple positive.
  • Triple Negative: If the breast cancer cells do not have estrogen receptors, progesterone receptors, or a larger than normal amount of HER2 receptors, the cancer cells are called triple negative. Learn about a possible treatment option that is used with chemotherapy for patients with certain types of advanced Triple Negative Breast Cancer (TNBC).

Ask your doctor about your breast cancer stage

Because of the many factors that help determine the stage of breast cancer, there are many different combinations that can make up each stage. In fact, two people can be the same stage but have different factors that lead to that stage.

Your doctor can talk to you about how your breast cancer stage was determined and how it’s being used to plan the best treatment for you.