Selective Estrogen Receptor Degraders (SERDs) for Breast Cancer

SERDs, also known as selective estrogen receptor downregulators or degraders, are a type of hormonal therapy used to treat advanced-stage, hormone receptor-positive, HER2-negative breast cancer.

SERDs, like selective estrogen receptor modulators (SERMs), block estrogen from attaching to cancer cells in the breast. By sitting in the estrogen receptors in and on hormone receptor-positive breast cancer cells, SERDs stop estrogen from signaling the cells to grow. SERDs also reduce the number of estrogen receptors and change the shape of the receptors so they don’t work as well.

There are two SERDs doctors use to treat breast cancer: Faslodex  (chemical name: fulvestrant) and Orserdu (chemical name: elacestrant).

You may be prescribed Faslodex if:

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  you’ve been diagnosed with advanced-stage, hormone receptor-positive, HER2-negative breast cancer and have been through menopause. 

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  you received a different hormonal therapy medicine and the breast cancer grew during treatment.

In some cases, Faslodex may be prescribed to men and pre- or post-menopausal women along with other targeted therapy medicines. If pre-menopausal women are prescribed Faslodex, they also receive medicine to stop their ovaries from functioning. Faslodex is given as two injections, one in each butt cheek.

You may be prescribed Orserdu if you’ve been diagnosed with advanced-stage, estrogen receptor-positive, HER2-negative breast cancer with an ESR1 mutation that has grown during or after treatment with a different hormonal therapy medicine. The medicine is commonly prescribed to men or post-menopausal women. Orserdu is a pill taken by mouth.

When advanced-stage, hormone receptor-positive HER2-negative breast cancers stop responding to hormonal therapy, it may mean the cancer has developed a mutation in the ESR1 gene. The ESR1 gene makes estrogen receptors. It’s estimated that up to 40% of advanced-stage estrogen receptor-positive, HER2-negative breast cancers develop an ESR1 mutation, mainly after treatment with an aromatase inhibitor. Besides making the cancer resistant to certain hormonal therapy medicines, ESR1 mutations also can make the cancer more likely to grow and spread.

Like all hormonal therapy medicines, SERDs may cause side effects, some of them severe. Some of the most common side effects of SERDs are bone and joint pain, nausea, fatigue, and vomiting.

Before starting a SERD, it’s a good idea to discuss possible side effects of the medicine with your doctor. Certain conditions — including a history of bleeding disorders and high cholesterol — can increase the risk of more severe side effects when taking a SERD.

During treatment, it’s also important to talk with your doctor if you’re experiencing troubling side effects, as they may have ideas about how to help you manage these symptoms.