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Elacestrant (Orserdu) is a hormonal therapy used to treat metastatic breast cancer. Elacestrant is part of a class of drugs called selective estrogen receptor degraders (SERDs), also known as an estrogen receptor antagonists (ERAs). These medicines stop estrogen from helping hormone receptor-positive breast cancer cells to grow. Elacestrant is the second drug of this kind to be approved by the Food and Drug Administration (FDA); it is the only one available as a pill. The first approved SERD to treat breast cancer was fulvestrant (Faslodex).

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How elacestrant works

Elacestrant is a hormonal therapy that was FDA approved in January 2023. It attaches to the estrogen receptors on hormone receptor-positive cancer cells, blocking estrogen's ability to attach to the cells and help them grow. As a SERD, elacestrant is also able to break down or weaken the estrogen receptor, making it inactive.

Elacestrant is the second SERD to be approved as a treatment for breast cancer. Fulvestrant was first approved in 2002. Elacestrant is a pill (an oral SERD); fulvestrant is given by injection. When used alone, elacestrant was more effective than fulvestrant in clinical trials. One reason for this is that the oral formula is absorbed into the body more easily.

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Who gets elacestrant

Elacestrant is an FDA-approved treatment for advanced or metastatic estrogen receptor-positive, HER2-negative breast cancer in postmenopausal women and adult men whose cancer:

  • Progressed on another hormonal therapy
  • Tests positive for an ESR1 gene mutation

Elacestrant is available to people who have already tried another hormonal therapy, either an aromatase inhibitor or fulvestrant. The first hormonal therapy was likely given with a CDK 4/6 inhibitor, a kind of targeted therapy. This combination is a standard first-line treatment for advanced or metastatic estrogen receptor-positive, HER2-negative breast cancer. It is often effective at first, but eventually stops working. The cancer can become resistant to one or both treatments in this combination. This resistance may be due to changes to the ESR1 gene. Elacestrant offers a next treatment option for if or when this occurs.

The FDA does not mention past use of CDK 4/6 inhibitors in the approval of elacestrant. However, there is a relationship between the length of time on a prior CDK 4/6 inhibitor drug and how well elacestrant works. In the clinical trial that led to FDA approval, all participants had previously taken a CDK 4/6 inhibitor. Researchers found that the longer a person had taken a CDK 4/6 inhibitor, the greater the benefit of elacestrant. Elacestrant was much more effective for people who had previously taken a CDK 4/6 inhibitor for 12 or more months, and even more effective after 18+ months. Yet even people who had taken a CDK 4/6 inhibitor for less than 6 months still saw benefit from elacestrant.

Elacestrant is also more effective against cancers that test positive for an ESR1 mutation. ESR1 is a gene associated with estrogen response. Over time, the ESR1 gene can change or mutate. An ESR1 mutation develops in many advanced or metastatic breast cancers. An ESR1 mutation can cause a tumor to become resistant to aromatase inhibitors, another kind of hormonal therapy. Until now, when this occurred, fulvestrant would be given next with little success.

When the FDA approved elacestrant, it also approved a test for the ESR1 mutation. The Guardant360 CDx assay is a blood test. The results are available in 7 days. The test results will let you and your doctor know whether you are a candidate for elacestrant.

If you are already on a treatment that is working, your doctor may advise continuing with it for now. ESR1 mutations develop over time. For this reason, ESR1 testing is recommended for estrogen-receptor positive cancers that continue to grow or spread after treatment with CDK 4/6 inhibitors.

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How elacestrant is given

Elacestrant is a pill that you take by mouth at the same time every day. It must be swallowed whole and taken with food. In contrast, the similar drug fulvestrant is given by injection to the buttocks by a doctor or nurse every 2 weeks.

Elacestrant can be taken for as long as it continues to work and does not cause harmful or unbearable side effects.

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Side effects & things to remember


Most people taking elacestrant find the side effects to be manageable. Nausea is the most common side effect. In the clinical trial that led to the drug’s approval, most people who experienced nausea were able to manage it without anti-nausea medicine.

Common side effects include:


While elacestrant is generally very safe, there is some risk of serious increased fat (lipids) in the blood. Your doctor will test your blood before and while on elacestrant to watch for this.

Elacestrant may not be given if you have liver problems or are pregnant, trying to become pregnant, or are the male partner of a female trying to become pregnant. Talk with your doctor about your options.

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Financial assistance for elacestrant


If you are considering taking elacestrant, reach out to your health insurance company to find out if the drug is covered, how long it may be covered, and what the out-of-pocket cost will be for you. If cost is a challenge, Stemline Therapeutics, the company that makes elacestrant, may be able to help. Through their patient support program, Stemline provides information and resources to help eligible individuals get started on the treatment. They also offer a rapid start program for people who are awaiting insurance approval. For information on patient support services or financial assistance programs, call 1-833-478-3654 (833-4-STEMLINE).

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Relevant disclosures: Dr. Kaklamani is a consultant for Menarini, Lilly, and Pfizer.

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Reviewed and updated: February 8, 2023

Reviewed by: Virginia Kaklamani, MD, DSc

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