What is Breast Cancer?

What is Breast Cancer?

Breast cancer affects over 280,000 women each year in the United States. Let's talk about how breast cancer is diagnosed, what its stages are, and how it's treated.

Medically reviewed by Susan Kerrigan, MD and Marianne Madsen


Breast cancer is one of the most talked-about cancers in the United States, with seemingly the whole country donning pink throughout October to raise awareness of the disease and funds for research. While there is a lot of awareness of the disease, it is important to understand more about the symptoms, treatments, and outcomes for those who have it.


Breast cancer symptoms


Finding a lump in your breast is often discussed as a sign of breast cancer. While that can be true, many women describe their breasts as lumpy or uneven as no breast is actually typical. They come in all shapes, sizes, and internal textures. They also can change in shape, size, or composition based on age, weight gain or loss, menstrual cycle, having children, or even certain medications. Just as breasts look and feel different for every person when they are non-cancerous, breast cancer symptoms can vary widely as well. Some people have no symptoms at all, while others may have some or all of these:


  • A newly formed lump in the breast or the armpit
  • A breast that becomes thicker or swollen
  • The skin of the breast begins to dimple, like the skin of an orange, or becomes irritated
  • Flaky skin or redness of the nipple or any other part of the breast
  • The nipple becomes inverted
  • Discharge from the nipple other than milk, including blood
  • Changes in the shape or size of the breast
  • Pain anywhere in the breast 


If you are showing any of the signs of breast cancer, it is important to see your doctor, even if you have had a recent mammogram that came back with normal results.


Breast cancer diagnosis


Doctors have several ways to diagnose breast cancer that involve varying degrees of invasiveness. A general practitioner may refer a patient to a breast specialist or a surgeon, but that does not mean the patient has breast cancer or will need surgery. Those specialists, though, are well-versed in the tools available to diagnose breast cancer. They are:


  • Ultrasound: This machine is used to make pictures, called sonograms, of the tissue inside the breast.
  • Diagnostic mammogram: This is different from a typical mammogram in that it is used to get a more detailed X-ray look at areas of your breast that may have appeared abnormal, lumpy, or problematic in a screening mammogram.
  • MRI: An MRI, or magnetic resonance imaging, is a body scan that uses a magnet to create highly detailed pictures of the internal tissues of the breast and send them to a computer for a technician and doctors to see.
  • Biopsy: While the other three tests are done externally, a biopsy is a procedure that removes tissue or fluid from a person’s breast to be looked at under a microscope and to be run through additional tests.


Breast cancer stages


Once breast cancer is diagnosed using one or a combination of the tests above, the doctor will then stage the breast cancer to determine how far the cancer has spread. Staging is a fairly complex system that uses seven factors that combine to create five general stages, each of which have sub-stages. 


The seven factors are:


  • Size of the tumor (T): Doctors will determine how large the tumor is and if it has grown into nearby locations.
  • Spread to nearby lymph nodes (N): Doctors will see if the cancer has spread to surrounding lymph nodes and how many lymph nodes it has spread to.
  • Spread to far-away sites, called metastasis (M): Doctors will see if the cancer has spread to areas far from the breasts, such as the liver, lungs, or brain.
  • Estrogen Receptor (ER) status: Doctors will look to see if the cancer has a protein referred to as an Estrogen Receptor.
  • Progesterone Receptor (PR) status: Doctors will look to see if the cancer has a protein referred to as a Progesterone Receptor.
  • HER2 status: Doctors will determine whether the cancer makes too much of the HER2 protein.
  • Grade of the cancer (G): Doctors will see whether the cells look like normal cells.


Once those seven factors are determined, doctors will then provide a stage for the cancer, ranging from Stage 0 to Stage IV.


Stage 0: This is used to describe non-invasive breast cancers, meaning they have stayed in one small area of the breast, such as DCIS (ductal carcinoma in situ). This stage means the cells have not broken away from their original location and they have not begun invading surrounding tissue.


Stage I: This describes an invasive breast cancer, meaning that the cancer cells have broken away from their initial location and are spreading to neighboring breast tissue. There are two subcategories, IA and IB, and they are based on the size and whether the cancer has spread to the lymph nodes. IB indicates a larger tumor that has spread to lymph nodes. 


Stage II: This stage is divided into stage IIA and stage IIB. 

Stage IIA is used to describe invasive breast cancer that meets one of these criteria: 

  • No tumor is found in the breast, but cancer is found in nearby lymph nodes under the arm or near the breastbone
  • The tumor is 2 centimeters or less and the cancer has spread to the lymph nodes
  • The tumor is between 2 and 5 centimeters but has not spread to the lymph nodes–if the tumor is between those sizes but has not spread and is HER2-negative

Stage IIB is used to describe invasive breast cancer that meets these criteria:

  • The tumor is between 2 and 5 centimeters and cancer cells have spread to the lymph nodes
  • The tumor is larger than 5 centimeters but cancer cells have not spread to the lymph nodes


Stage III: This stage is divided into three stages: Stage IIIA, stage IIIB, and stage IIIC.

Stage IIIA is based on how large the tumor is and how many lymph nodes it has spread to. The cancer must meet one of these criteria to be stage IIIA:

  • No tumor is found, or a tumor of any size is found, but cancer is detected in 4 to 9 lymph nodes under the arm or near the breastbone
  • The tumor is larger than 5 centimeters and small clumps of cancer cells are found in 1 to 3 of the lymph nodes under the arm or near the breastbone

Stage IIIB is diagnosed if cancer has:

  • Spread to the chest wall and has caused swelling or an ulcer
  • Spread to up to 9 lymph nodes under the arm or any lymph nodes along the breastbone

Stage IIIC cancer is diagnosed if:

  • Cancer has spread to 10 or more lymph nodes under the arm
  • Cancer has spread to the lymph nodes found near the collarbone


Stage IV cancer is cancer that has spread to other parts of the body, such as the lungs, lymph nodes located far away from the breast, bones, skin, liver, or brain. Cancer can be stage IV at initial diagnosis which is referred to by doctors as “de novo,” or it can be breast cancer that has recurred and spread to other parts of the body.


Chances of remission or recurrence


It is common for people who have been diagnosed with breast cancer to head straight to the internet to look for statistics on the chances that the cancer goes away, called remission, or how likely it is for the cancer to reoccur. However, it is important to recognize that there are many factors that play into these rates, including genetics and treatment options pursued. With that said, the Surveillance, Epidemiology, and End Results (SEER) database, which is hosted by the National Cancer Institute, provides insight into these rates.


The SEER uses the terms localized, regional, and distant to describe how far the cancer has spread. For people who have localized cancer, the five-year survival rate is 99%. For those with regional cancer, the survival rate is 86%, and for those with distant cancer, the rate is 28%.


For how often cancer comes back, if a person has localized cancer but has a lumpectomy and radiation treatment, their chances of having the cancer return is between 3 and 15% with the combined treatments. For those who have a mastectomy, there is a 6% chance of getting cancer again in five years if no lymph nodes were involved. For those whose lymph nodes were involved, there is a 25% chance of the cancer coming back, but that drops to 6% if the patient also undergoes radiation therapy.