Breast Cancer 101

Breast Cancer 101

Being diagnosed with breast cancer is overwhelming to say the least. There are a multitude of terms you may hear regarding your cancer and trying to figure out what it all means can be daunting. Some terms you may hear in the Doctor’s office are:

  • Stage 
  • Grade
  • Invasive vs Noninvasive
  • Hormone Receptor Status
  • HER2 Protein

Here we have laid out exactly what all of these common terms mean to give you a guide to breast cancer. Consider this your breast cancer 101. 

Breast Cancer Stages

The TNM staging system is the most commonly used when dealing with breast cancer. It stands for tumor, lymph nodes, and metastasis. It is broken down as follows:

Stage 0: When abnormal cells can be found in the milk ducts. 

Stage 1: Cancer can be confirmed, but it has not yet spread and the tumor is 2cm or smaller. 

Stage 2: The cancer has only grown to nearby lymph nodes and is still contained within the breast. The tumor is less than 5cm. 

Stage 3: This is considered an advanced stage. The tumor has grown beyond 5cm and cancer cells have invaded nearby lymph nodes and muscle. 

Stage 4: This advanced stage means that the cancer has spread to other areas of the body. 


The grade of your cancer refers to how aggressive the cells look to a pathologist when viewed under a microscope. This can reveal how fast they are growing and how quickly they can advance from one stage to another 

Invasive vs Noninvasive

Noninvasive cancers stay in the ducts or lobules and have not spread to surrounding tissues or other parts of the body. Noninvasive cancer can ultimately become invasive. 

Invasive breast cancer has spread from the milk duct into the breast tissue. 

Hormone Receptor Status

ER-positive:  Estrogen-receptor-positive (ER+) means the cancer has receptors for estrogen. Data shows that when cancer cells are ER+, they receive signals from estrogen that promotes growth.

PR-negative:  Progesterone-receptor-positive (PR+) is when the cancer cells have progesterone receptors. These cells can be influenced by progesterone which can promote growth.

Hormone-Receptor-Negative:  This is when the cancer cells have no receptors, meaning hormonal therapy is unlikely to work.

Roughly 66% of breast cancers have hormone receptors.1

HER2 Protein

HER2-positive breast cancer is when the cells test positive for a protein called human epidermal growth factor receptor 2 (HER2). This protein can promote cancer growth.

About 20% of patients with breast cancer have a gene mutation that causes the HER2 protein to be made in excess.2 While this type of cancer can be more aggressive, patients can still benefit from hormone therapy.