Estrogen Receptor Downregulators (ERD)

What are Estrogen Receptor Downregulators (ERDs)

Estrogen Receptor Downregulators are a type of hormonal therapy. Currently, the only drug in this class that is approved for used by the USFDA is called fulvestrant. It is indicated in hormone receptor-positive breast cancer.

How are ERDs administered?

Fulvestrant is given as an intramuscular injection, similar to a vaccine as opposed to a tablet or pill. The most common injection site is the buttocks and it is given once a month, making it very well-tolerated. Your doctor will monitor you closely while you are receiving the injections.

What do ERDs do?

Similar to the action of SERMs, ERDs bind to estrogen receptors on the surface of breast cells. In doing so, they too prevent estrogen from sending a signal into the cell that allows the cell to grow and divide. The two main actions of ERDs are to:

  • Decrease the total amount of estrogen receptors on the cell surface
  • Alter the shape of the estrogen receptor so that estrogen cannot bind correctly, preventing proper function

When is ERD Hormonal Therapy Indicated Breast Cancer Treatment?

This drug is indicated for hormone receptor-positive breast cancer and has been shown to be most beneficial in postmenopausal women. Moreover, it is approved for use when metastatic (advanced-stage) hormone receptor-positive breast cancer is diagnosed, and the cancer is no longer responsive to other hormonal therapy drugs. Alternatively, your doctor may recommend this drug if the side effects of other kinds of hormonal therapy drugs become intolerable.

Who should not take ERDs for Breast Cancer Treatment?

Fulvestrant is not recommended for use in any of the following cases:

  • Allergy to the drug
  • Pregnancy or breast feeding – this drug can be harmful to the fetus, causing a variety of birth defects
  • Liver disease
  • Clotting disorders (tendency to clot)
  • Low platelets
  • Hormone receptor-negative breast cancer

If you have any of the above conditions, you and your doctor will need to discuss whether or not the benefits of taking the drug will outweigh the risks.

Research has indicated the ERDs are as effective as other forms of hormonal therapy in preventing recurrence and slowing growth of cancer. It has been found to be superior to the aromatase inhibitor, anastrozole, in its ability to slow or even prevent the spread of metastatic breast cancer cells in postmenopausal, hormone-receptor-positive breast cancer patients. Research in 2002 showed that when Tamoxifen (SERM) is no longer effective, ERDs have been successful in slowing cancer growth in some cases.[1]

What are the Side Effects of ERDs?

As with any drug, ERDs are not without side effects. The following is a list of potential side effects that may be experienced with ERD use.

  • Nasusea
  • Vomiting
  • Constipation
  • Diarrhea
  • Abdominal pain
  • Hot flashes
  • Sore throat
  • Back pain
  • Headache
  • Pain at the injection site

The following side effects do occur but are less common:

  • Bone pain
  • Dizziness
  • Dry skin
  • Joint pain
  • Loss of appetite
  • Nervousness
  • Swelling
  • Sleeping difficulties
  • Sweating


ERDs are a type of hormonal therapy that may be effective in some breast cancer patients. You and your doctor can determine if they are an option in your breast cancer treatment regimen.


1 Osborne, CK; Pippen, J; Jones, SE; Parker, LM; Ellis, M; Come, S; Gertler, SZ; May, JT; Burton, G; Dimery, I; Webster, A; Morris, C; Elledge, R; and Buzdar, A. (2002).  Double-Blind, Randomized Trial comparing the Efficacy and Tolerability of Fulvestrant Versus Anastrozole in Postmenopausal Women with Advanced Breast Cancer Progressing on Prior Endocrine Therapy: Results of a North American Trial. J Clin Oncology, 20(16):3386-95.

This article was originally published on July 27,2012 and last revision and update of it was 9/2/2015.