Role of Estrogen Receptors in Breast Cancer

The hormone receptors are the “eyes” and “ears” of the cells.

Before understanding what estrogen receptors are, let us know what are receptors.

Cell receptors, including hormone receptors, are special types of proteins that are found within or on the surface of cells. They are spread throughout the body and can attach to certain substances in the blood. 

The hormone receptors are the “eyes” and “ears” of the cells. They carry the function of receiving messages from substances in the bloodstream and then telling the cells what to do. A mechanism known as activation (upregulation) and deactivation (downregulation) of the receptors is responsible for many functions in the body.

Estrogen receptors (ERs) are receptors that are activated by the hormone estrogen (one of the female sex hormones). They are found most commonly in the inner lining of the uterus (endometrium), breast cells, ovarian cells, and a part of the brain (the hypothalamus). In males, they are found in the ducts (efferent ducts) attached to the testes. Some have also been found in the kidney, brain, bone, heart, lungs, intestine, and prostate.

When estrogen and/or progesterone attach (bind) to their specific hormone (estrogen or progesterone) receptors, they help contribute to the growth and function of breast cells. Estrogen and progesterone are female hormones playing a key role in the sexual and reproductive cycle of women. These hormones are also found in men but exist in smaller quantities.

The ER is also a target of growing interest to develop medicines for osteoporosis, breast cancer, and other endocrine female disorders.

Breast cancer cells removed during a biopsy or breast surgery will be tested to see if they have estrogen or progesterone receptors. When the hormones estrogen and progesterone attach to these receptors, they accelerate cancer growth. 

The terms “hormone receptor-positive” or “hormone receptor-negative” are used for specifying the hormone receptor status of a person with breast cancer. If the person has estrogen hormone receptors, their breast cancer is termed estrogen receptor-positive breast cancer, and if they do not have them, it is termed estrogen-negative breast cancer. Treatments for breast cancer will depend on its hormone status. A patient can ask their doctor about their hormone status to know what kind of treatment they would most likely receive.

A test called immunohistochemistry helps find out if the breast cancer cells have estrogen receptor (ER) and progesterone receptor (PR). The test results will help guide the doctor (oncologist or surgeon) to plan the treatment for a patient with breast cancer

• Hormone receptor-positive (or hormone-positive) breast cancer cells have either ER or PR or both. The treatment for this type of breast cancer involves hormone therapy drugs that lower estrogen levels or block ER (preventing estrogen from acting on the breast cancer cells). 
• Hormone receptor-negative (or hormone-negative) breast cancer cells have neither ER nor PR. This type of breast cancer is more common in menopausal women. Hormone therapy is not effective, and surgery usually remains the primary treatment.
• Triple-negative breast cancer cells don’t have ER or PR and also don’t make too much of human epidermal growth factor receptor 2 (HER2) (a growth-promoting protein on the outside of all breast cells). Both hormonal drugs and drugs that target HER2 are ineffective in treating this type of cancer. Doctors generally consider chemotherapy, radiation therapy, or surgery.
• Triple-positive cancer cells are ER-positive, PR-positive, and HER2-positive. These cancers can be treated with hormonal therapy as well as drugs that act on HER2.