top of page
what is breast cancer

What is Breast Cancer? 

Sand Dunes

What is Breast Cancer? 

Breast cancer is an uncontrolled growth of breast cells. To better understand breast cancer, it helps to understand how any cancer can develop. 


Cancer occurs as a result of mutations, or abnormal changes, in the genes responsible for regulating the growth of cells and keeping them healthy. The genes are in each cell’s nucleus, which acts as the “control room” of each cell. Normally, the cells in our bodies replace themselves through an orderly process of cell growth: healthy new cells take over as old ones die out. But over time, mutations can “turn on” certain genes and “turn off” others in a cell. That changed cell gains the ability to keep dividing without control or order, producing more cells just like it and forming a tumor.


A tumor can be benign (not dangerous to health) or malignant (has the potential to be dangerous).

Benign tumors are not considered cancerous: their cells are close to normal in appearance, they grow slowly, and they do not invade nearby tissues or spread to other parts of the body. Malignant tumors are cancerous. Left unchecked, malignant cells eventually can spread beyond the original tumor to other parts of the body.


The term “breast cancer” refers to a malignant tumor that has developed from cells in the breast. Usually breast cancer either begins in the cells of the lobules, which are the milk-producing glands, or the ducts, the passages that drain milk from the lobules to the nipple. Less commonly, breast cancer can begin in the stromal tissues, which include the fatty and fibrous connective tissues of the breast.


Breast Anatomy.

A breast is made up of three main parts: lobules, ducts, and connective tissue. The lobules are the glands that produce milk. The ducts are tubes that carry milk to the nipple. The connective tissue (which consists of fibrous and fatty tissue) surrounds and holds everything together. Most breast cancers begin in the ducts or lobules.


Over time, cancer cells can invade nearby healthy breast tissue and make their way into the underarm lymph nodes, small organs that filter out foreign substances in the body. If cancer cells get into the lymph nodes, they then have a pathway into other parts of the body. The breast cancer’s stage refers to how far the cancer cells have spread beyond the original tumor (see the Stages of breast cancer below for more information).


Breast cancer is always caused by a genetic abnormality (a “mistake” in the genetic material). However, only 5-10% of cancers are due to an abnormality inherited from your mother or father. Instead, 85-90% of breast cancers are due to genetic abnormalities that happen as a result of the aging process and the “wear and tear” of life in general.

There are steps every person can take to help the body stay as healthy as possible, such as eating a balanced diet, maintaining a healthy weight, not smoking, limiting alcohol, and exercising regularly (learn what you can do to manage breast cancer risk factors). While these may have some impact on your risk of getting breast cancer, they cannot eliminate the risk.


Developing breast cancer is not your or anyone's fault. Feeling guilty, or telling yourself that breast cancer happened because of something you or anyone else did, is not productive. 

Stages of Breast Cancer

Staging is a standard term used across the medical profession to communicate how widespread or advanced the cancer is in the breast tissue and possibly other parts of your body. 

If you are diagnosed with breast cancer, doctors and pathologists will examine biopsy and imaging results to determine the stage — also known as the progression — of the disease.


The process is complicated but necessary to determine the best treatment plan for your particular type of cancer. The most common staging system is the TNM (Tumor, Node, Metastasis - more on this below), which focuses on tumor size, lymph node involvement and metastatic spread of the cancer. It also factors in details related to hormone receptors, the protein HER2 and growth rate of the cells.


The staging of your tumor is utilized by doctors to explain the breadth and scope of the cancer and helps them determine how to move forward with treatment, including surgery, if needed.  


Doctors use diagnostic tests to find out the cancer's stage, so staging may not be complete until all the tests are finished.  The stage of a breast cancer is determined by the cancer’s characteristics, such as how large it is and whether or not it has hormone receptors. The stage of the cancer helps you and your doctor:

•         figure out your prognosis, the likely outcome of the disease

•         decide on the best treatment options for you

•         determine if certain clinical trials may be a good option for you


Breast cancer stage is usually expressed as a number on a scale of 0 through IV — with stage 0 describing non-invasive cancers that remain within their original location and stage IV describing invasive cancers that have spread outside the breast to other parts of the body.

Clinical vs. Pathological Staging

Clinical staging is based on the results of tests done prior to surgery.  If your biopsy comes back positive, your doctor may order additional tests to garner a better understanding if and where the cancerous cells have spread.  This data gathering period may include physical examinations, mammogram, ultrasound, and MRI scans.  In some cases your doctor may also order a bone or CT scans. 


Pathologic staging is based on what is found during surgery to remove breast tissue and lymph nodes.  While a lot of the aforementioned tests can provide your oncological team with lots of information and data points, it is not until surgery is performed whereby the surgeons can remove the tumor and possible lymph nodes in order to confirm the size of the tumor, the number of lymph node involvement, and whether or not the cancer has metastasized. 


Early Stage Breast Cancer

Early stage breast cancer refers to stages 0-III. 


Stage 0

Stage 0 cancers are called “carcinoma in situ.” Carcinoma means cancer and “in situ” means “in the original place.” Types of “in situ carcinoma” include

•           DCIS – Ductal carcinoma in situ

•           LCIS – Lobular carcinoma in situ

•           Paget disease of the nipple


Stage I

Stage I can be divided into Stage IA and Stage IB. The difference is determined by the size of the tumor and the lymph nodes with evidence of cancer.


Stage II

Stage II means the breast cancer is growing, but it is still contained in the breast or growth has only extended to nearby lymph nodes.


This stage is divided into groups: Stage IIA and Stage IIB. The difference is determined by the size of the tumor and whether the breast cancer has spread to the lymph nodes.


Stage III

Stage III cancer means the breast cancer has extended beyond the immediate region of the tumor and may have invaded nearby lymph nodes and muscles, but has not spread to distant organs.  


This stage is divided into three groups: Stage IIIA, Stage IIIB, and Stage IIIC. The difference is determined by the size of the tumor and whether cancer has spread to the lymph nodes and surrounding tissue.


Stage IV


In Stage IV, the cancer has spread to other organs and parts of the body beyond the breast. This stage is often referred to as metastatic breast cancer (MBC) and is more difficult to treat due to the impact on other organs. Stage IV cancer symptoms include visible swelling in the breast and armpit; dry, flaky skin; red, dimpled skin; nipple discharge; breast pain; fatigue; insomnia; loss of appetite; weight loss; shortness of breath and other symptoms related to the specific organs involved.


Although Stage IV breast cancer is not curable, it is treatable to a certain extent and current advances in research and medical technology mean that more and more women are living longer by managing the disease as a chronic illness with a focus on quality of life as a primary goal. With excellent care and support, as well as personal motivation, Stage IV breast cancer may respond to a number of treatment options that can extend one’s life for several years.



TNM Staging System

Doctors use the TNM system to ensure that medical professionals are using the same language and system to describe the tumor. 


refers to the size of the tumor measured in centimeters and where it is located.


N refers to the number of lymph nodes which were positive for cancer. If no lymph nodes were involved, the pathology report would state N(0).


M refers to whether or not the cancer has traveled to distant part of the body such as the bones or organs. If it has spread, it will state where and how much. 


As an example, stage IIB may read something like this:  (T3, N0, M0) meaning the tumor is greater than 55mm and has not spread to the lymph nodes or other parts of the body. 


Updated Staging Guidelines

The American Joint Committee on Cancer (AJCC) established the way cancer is communicated. Clinicians and the surveillance community count on the AJCC for the most comprehensive anatomic staging data available, I.e., the Cancer Staging Manual and Cancer Staging Atlas.

In 2018 the AJCC updated the breast cancer staging guidelines to add other cancer characteristics to the T, N, M system to determine a cancer’s stage.


In addition to knowing the stage of your cancer, breast cancer is also classified according to other characteristics. These include how sensitive it is to the hormones estrogen and progesterone as well as to the level of certain proteins that play a role in breast cancer growth, such as HER2. It is also classified by the cancer’s genetic makeup.


•           Tumor Grade: a measurement of how much the cancer cells look like normal cells


•           Estrogen- & Progesterone-Receptor Status: do the cancer cells have receptors for the hormones estrogen and progesterone?


•           HER2 status: are the cancer cells making too much of the HER2 protein?


•           Oncotype DX score, if the cancer is estrogen-receptor-positive, HER2-negative, and there is no cancer in the lymph nodes.


The above amended guidelines have helped to create and reinforce ontological/surgical treatment advances.  As you can imagine Staging is a complex undertaking and these latest AJCC guidelines allow for a more cohesive and universal diagnosis and treatment options.


References and additional information on staging can be found on the resource links below:

breast, breast cancer stages

Breast Cancer Stages

Early Stage Breast 

Early stage breast cancer refers to stages 0-III

Late Stage or Advanced Stage Breast Cancer

Late stage breast cancer refers to stage IV, or Metastatic Breast Cancer (MBC)

types of breast cancer, bust

Types of Breast Cancer

Breast cancer is not just one disease — it can be classified into different types depending on how the cells in the breast look under a microscope. Different types of breast cancer include:

1. Ductal Carcinoma In Situ (DCIS): DCIS is considered a non-invasive form of breast cancer, meaning it has not spread beyond the milk ducts into any surrounding normal tissue. Check out Jennifer's story being diagnosed with DCIS after a clear mammogram. 


2. Invasive Ductal Carcinoma (IDC): This is the most common type of breast cancer, where cancer cells have invaded the surrounding tissue.


3. Inflammatory Breast Cancer: This type of breast cancer is considered aggressive and can often be hard to diagnose because it does not always form a lump.


4. Lobular Carcinoma In Situ (LCIS): LCIS is considered a non-invasive type of breast cancer which means that the cancer cells are contained within the lobules and have not spread to surrounding normal tissue.


5. Invasive Lobular Carcinoma (ILC): This type of cancer starts in the milk-producing lobules and can spread beyond them into other parts of the breast.


6. Mucinous Carcinoma: This type of breast cancer is slow growing and therefore often less aggressive. It starts in the main cells of mucus, called mucin. Although this type of cancer can develop anywhere, it's most common in your breast.


7. Metaplastic Breast Cancer: MpBC is an aggressive and invasive type of cancer, meaning that it multiplies quickly and can spread throughout the body. MpBC tends to spread or metastasize more than other breast cancers.

8. Angiosarcoma: This type of cancer is very rare and can occur in any part of the body, but it is most commonly found in the breast tissue.


9. Phyllodes Tumor: This type of tumor is not considered cancer, but it can still be dangerous if not treated promptly.


10. Paget's Disease: This is a rare form of breast cancer that starts in the nipple and can spread to other parts of the breast if left untreated.

Questions to Ask Your Surgeorn

Understanding the Different Types of Breast Cancer

Connect with Others during our Weekly Virtual Meet-Up

bottom of page