What Is HR and HER2 Breast Cancer?

Breast cells express certain proteins on their surface called hormone receptors (HRs) that act as binding sites to the hormones estrogen or progesterone. This binding or reception of signals from the hormone results in the increased growth of breast cells. 

Breast cancer occurs when there is an uncontrolled growth of cells in the breast. Due to certain abnormalities, certain breast cancer cells may not respond to the various regulators of cell growth and division and thus may not carry HRs for estrogen (ER), progesterone (PR), or both:

• HR− breast cancer occurs when the cancer cells carry none of the HRs
• HR+ breast cancer occurs when the cancer cells carry either or both of the HRs

Almost 66% of breast cancer cases are HR+. Of the HR+ cases, about 80% are either ER+ or both ER/PR+.

Another receptor protein that is present on the breast cell surface is called the human epidermal growth factor receptor 2 (HER2) receptor. It is sometimes called the HER2/neu receptor and helps in the growth, division, and repair of breast cells. 

Some breast cancer cells may have a genetic mutation called HER2 gene amplification, which may cause the overexpression of HER2 receptors. This makes cancer cells multiply rapidly. 

Breast cancer cells with HER2 protein overexpression are called HER2+ breast cancer. About 10%-20% of breast cancer are HER2+.

Triple negative breast cancer (TNBC) means that the cancer cells do not have estrogen (ER) and progesterone (PR) on their surface, and they do not over-express the HER2 protein as well (HER2−). In contrast to TNBC, triple positive breast cancer means the cancer cells are ER+, PR+, and HER2+.

TNBC accounts for about 10%-15% of breast cancer cases. Patients with TNBC tend to have a worse outcome compared to those with other types of breast cancer due to the following factors:

• TNBC tends to grow more rapidly and aggressively
• There are fewer treatment options for TNBC

Factors that may increase the risk of this type of breast cancer include:

• Age (women younger than 40 are more likely to have TNBC than older women)
• African American ethnicity
• BRCA1 mutation (BRCA1 is a type of gene associated with certain types of cancer such as breast, ovarian, prostate, and pancreatic cancer)

Knowing the hormone receptor (HR) status is important in planning breast cancer treatment and predicting prognosis. 

If breast cancer is HR+, medications can be given to block particular HRs on breast cancer cells. Blocking the receptor means that the cancer cells will not grow and multiply in response to the hormones and will eventually die or slow their growth. 

Additionally, medications may be administered to lower estrogen levels, which will help limit the growth of HR+ cancer cells. If, however, the cancer cells are negative for both estrogen (ER) and progesterone (PR), these hormone drugs will not be effective. Furthermore, if the cancer cells are HER2−, medications that target HER2 receptors cannot be used. 

HR+ breast cancer tends to have a better prognosis than HR− breast cancer.

Doctors can confirm whether you have HR+ or HR− cancer through an immunohistochemistry test. For this test, a biopsy is done to collect a sample of tumor tissue and send it to a lab for examination. 

A similar test can be done to determine whether breast cancer is HER2+ or HER2−. A part of the HER2 protein may be shed from the surface of breast cancer cells. This can be detected in a serum using a method called enzyme-linked immunosorbent assay.