​ ​ breast cancer glossary & terms - Breast Connect
Breast cancer glossary & terms

There’s a whole new language you will learn once diagnosed with breast cancer. We have listed links to some excellent glossaries and descriptions, but before you get started, we have provided some basic terms for you to get you on your way.




Ductal Carcinoma In Situ is the earliest form of diagnosed breast cancer. Cells have been identified within the milk ducts as cancerous, but have yet to leave those contained areas.  These patients have an excellent prognosis and multiple treatment options based upon their personal needs and doctor’s suggestions: lumpectomy and radiation, mastectomy and reconstruction, and/or hormone therapies are common.  Remember that what is right for you might not be right for the next patient.



Invasive Ductal Carcinoma, also known as infiltrating ductal carcinoma, is the most common form of breast cancer. This cancer starts as cells in the milk ducts and spreads to the other breast tissues. Over time, it can also spread beyond the breast.



Invasive Lobular Carcinoma is the second most common type of breast cancer. This cancer starts in the milk-making lobules which empty out into the ducts that carry milk to the nipple.  ILC is more common in older women, but not exclusively! It may also be more difficult to see under routine imaging. Left untreated, this cancer can spread outside the breast.

To learn more about the types of breast cancer, visit BreastCancer.org.



Your pathology report will include the results of a hormone receptor assay, a test that tells you whether or not the breast cancer cells have receptors for the hormones estrogen and progesterone. Hormone receptors are proteins — found in and on breast cells — that pick up hormone signals telling the cells to grow.


ER-/+ or PR-/+

You may hear the term Estrogen Receptor Negative/Positive or Progesterone Receptor Negative/Positive. During your diagnosis, you may have a test called an IHC (ImmunoHistoChemistry).  Most breast cancers are ER+ and PR+.  That means that the cancer cells have receptors that “like” estrogen and progesterone. You will probably need some kind of hormone therapy that blocks your body’s hormones and therefore lowers your risk for cancer recurrence. If your tests come back with a negative, hormone therapy is probably not recommended, but other types of treatment may be suggested.



The HER2 gene makes HER2 proteins. HER2 proteins are receptors on breast cells. Normally, HER2 receptors help control how a healthy breast cell grows, divides, and repairs itself, but in about 25% of breast cancers, the HER2 gene doesn’t work correctly and makes too many copies of itself (known as HER2 gene amplification). All these extra HER2 genes tell breast cells to make too many HER2 receptors (HER2 protein overexpression). This makes breast cells grow and divide in an uncontrolled way.  HER2 positive breast cancers tend to grow faster and are more likely to spread and come back compared to HER2 negative breast cancers. But there are medicines specifically for HER2 positive breast cancers that are showing very positive results.


Here are some additional resources with more information on symptoms and definitions:

Lastly, even if you do not have metastatic breast cancer, check out the comprehensive  Insider’s Guide to Metastatic Breast Cancer by Anne Loeser, an MBC patient.  The booklet contains up-to-date information about the disease, standard and investigational treatments, coping with symptoms and side effects, and more.  As one reader stated,”It should be given to every woman immediately upon receiving a diagnosis of MBC.”



Most cancers are described by stages, and in breast cancer those stages are numbered 0 to 4. The higher the number, the more advanced the disease. While all forms of breast cancer should be taken very seriously, the earlier the diagnosed stage, the better the prognosis and the more choices a patient will have for treatments. The following is a very simple and brief synopsis of each stage (please note that there is far more complexity to cancer stages than what is written here):


Stage 0 

Commonly referred to as DCIS (Ductal Carcinoma In Situ), the cancer cells are still within the milk ducts and have likely not traveled to the surrounding tissue in the breast. It is also called noninvasive cancer.


Stage 1

The cancer cells have formed a tumor 2cm or less.  Stage 1A is defined as no lymph node involvement.  Stage 1B is defined as the same but with microscopic lymph node involvement of 2mm or less.


Stage 2

Stage 2A: The tumor is 2cm or smaller and has spread to the axillary lymph nodes, or the tumor is larger than 2cm and smaller than 5cm with no lymph node involvement. Stage 2B: The tumor is larger than 2cm and smaller than 5cm with 1-3 lymph node involvement or over 5cm without lymph node involvement.


Stage 3 

Cancer cells have left the tumor and have traveled toward lymph nodes. Stage 3A: The tumor is under 5cm with 4-9 lymph node involvement or over 5cm with 1-3 lymph node involvement. Stage 3B: The tumor has spread to the chest wall whether there is node involvement or not. Stage 3C: The tumor has 10+ node involvement.


Stage 4

Often referred to as “metastatic cancer,” cancer cells from the breast have set up shop in other parts of the body. The most common places include the lungs, liver, brain, and bones. Cancer can also be defined as stage 4 when it travels to distant lymph nodes or is fixed to the chest wall.

To learn more about breast cancer stages, visit NationalBreastCancer.org.