What Is Breast Cancer?

March 28, 2018

What Is Breast Cancer?

Having breast cancer means that some cells in your breast have changed and are growing out of control. Learning about the different types and stages of breast cancer can help you take an active role in your treatment decisions.

Changes in your breast

Your entire body is made of living tissue. This tissue is made up of tiny cells. You can't see these cells with the naked eye. Normal cells divide (reproduce) in a controlled way. They grow when your body needs them, and die when your body doesn't need them any longer. When you have cancer, some cells change or become abnormal. These cells divide quickly, don't die when they should, and can spread into other parts of the body.

Cross section of breast.

Cross section of breast showing noninvasive breast cancer.

Normal breast tissue is made of healthy cells. They divide to make new cells that look and work the same. The lobules make milk and the ducts carry it to the nipple.

Noninvasive breast cancer (called carcinoma in situ) happens when cancer cells are only in the ducts.

Cross section of breast showing invasive breast cancer.

Outline of woman from head to mid-thigh.  Arrows show breast cancer spreading to multiple organs.

Invasive breast cancer happens when cancer cells move out of the ducts or lobules into nearby breast tissue.

Metastasis happens when cancer cells move into the lymph nodes or bloodstream and travel to another part of the body.


Stages of breast cancer

Tests are used to learn more about the cancer. Genetic testing of the tumor is taken into account as well. This process is called staging. the stage of your cancer will help guide which treatment plan is best for you. Staging will give you this information:

  • The size of the tumor

  • If the cancer has spread to lymph nodes

  • If the cancer has spread to other parts of your body

  • Estrogen receptor (ER) status

  • Progesterone receptor (PR) status

  • Her2/new (Her 2) status

  • Grade of the cancer

This information is used to put breast cancers into groups. The groups range from 0 to 4 and are written as Roman numerals (0, I, II, III, IV). Stage 0 is the lowest stage. This means the cancer is only found in the lining of the breast duct. Stage 0 may also be called DCIS, or ductal carcinoma in situ. Stage IV is the highest stage and means the cancer has spread beyond the breast to other parts of the body. The other stages range in between.

The stages of breast cancer are very complex. But the more details know about each person's cancer, the better doctors are able to focus treatment. Talk to your doctor about your stage, what is means for you, and how it affects your treatment plan and long-term outcomes.


March 28, 2018


AJCC Cancer Staging Manual, Chapter 1, Principles of Cancer Staging (2017), Giuliano, AE., Breast Cancer Major changes in the American Joint Committee on Cancer, 8th edition, CA: A Journal for Clinicians (2017); 67(4); 290-303., Tumor, Node, Metastasis (TNM) staging classification for breast cancer, Up To Date

Reviewed By:  

Cunningham, Louise, RN,Stump-Sutliff, Kim, RN, MSN