Selective Estrogen-Receptor Modulators (SERMs)

Hormonal therapy is typically used as an adjunct to chemotherapy, radiation and surgery in the treatment of breast cancer. The three types of hormone therapy drugs are aromatase inhibitors, estrogen receptor downregulators (ERDs) and selective estrogen-receptor modulators (SERMs).

What are SERMs?

As the name implies, SERMs are drugs that bind estrogen receptors on the surface of breast cancer cells. They are referred to as “selective” because they bind only to estrogen receptors that are found in breast tissue. Since estrogen cannot bind the tissue in the breast, it may bind to other tissues of the body, such as liver, bone and uterus, which can cause side effects.

How do they work and what are some examples?

The function of SERMs is to bind specifically to the estrogen receptors in breast tissue, blocking estrogen from binding and preventing the cell from receiving the signals to grow and divide.

Currently, there are three SERMs that are used to treat breast cancer today.[1] These are:

  • Tamoxifen – the original SERM
  • Raloxifene – also a SERM, indicated for use in osteoporosis as well
  • Toremifene – newer SERM, approved by the FDA in 2007

These medicines are taken daily by mouth in the form of a pill for a total of five years. Postmenopausal women often have hormone receptor positive breast cancer, however, they are indicated in any patient that has hormone receptor positive cancer.

What are the Potential Side Effects?

The side effects of SERMs may vary by the individual, and is based on the drug used, dosage and the physical condition of the individual patient. The most common side effects from SERM use are:

  • Abdominal bloating – Raloxifene
  • Dry skin – Tamoxifen
  • Fatigue – Tamoxifen
  • Hot flashes  – all types of hormone therapy
  • Hypercalcemia – Toremifene
  • Mood swings – Toremifene
  • Night sweats – all types
  • Rash – Toremifene
  • Vaginal discharge – Toremifene
  • Water retention – Raloxifene

There are, however, also more serious potential risks from taking SERMS as part of your hormonal therapy. These include the following:

  • Abnormal vaginal bleeding or discharge
  • Blood clot formation – Tamoxifen and, rarely, Raloxifene
  • Bone or joint pain – Tamoxifen, Raloxifene
  • Breathing difficulties – Raloxifene
  • Depression – Tamoxifen
  • Endometrial cancer – Tamoxifen
  • Headache  – Raloxifene
  • Infertility and sexual dysfunction – Tamoxifen
  • Memory loss – Raloxifene
  • Blurry vision – Toremifene

The side effects of hormonal therapy can mimic those of menopause, since hormones are blocked from binding their receptor. Despite the many potential side effects, SERMs are quite effective as an adjunct in breast cancer treatment.

What are the Benefits?

Research has studied SERMs to discover their efficacy. In many instances, the studies have compared them to another form of hormonal therapy – aromatase inhibitors. The most common type of comparison has involved the ever popular tamoxifen. [2] The case studies usually focused on early stages of hormone-receptor-positive breast cancer. The patient of choice has been post-menopausal women. The conclusions generally indicate SERMs to be effective alone, but more effective when used as part of an ongoing program. Alternating between the two forms of hormonal therapy provides the best means of reducing the overall risk.

Research has also compared the effects and durability of Raloxifene against Tamoxifen. Indications are that the two SERMs are equally capable of performing their tasks effectively and efficiently. Yet, research also indicates the ability of SERMs hormonal treatment against cancer to have an effect that can last 15 years following the final treatment. In addition, taking SERMs can actually reduce your risk of osteoporosis and other bone-density problems. It alleviates this issue by increasing your bone density. Tamoxifen is specifically involved in enhancing skeletal strength.


SERMs are a viable form of hormonal therapy. It can treat both pre- and postmenopausal women effectively. It may be used alone, but it is far more effective when utilized as part of a comprehensive breast cancer treatment. Consult your medical professional about whether SERMs hormonal therapy will best serve your breast cancer treatment needs.


1 Ricks, D (2005). Breast Cancer Basics and Beyond. Alameda, CA: Hunter House, Inc.

2 Early Breast Cancer Trialists’ Collaborative Group (EBCTCG) (2011). Relevance of Breast Cancer Hormone Receptors and Other Factors to the Efficacy of Adjuvant Tamoxifen: Patient-Level Meta-Analysis of Randomised Trials. The Lancet, 378, (9793):771 – 784.

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