Fulvestrant

Fulvestrant (Faslodex) is an injectable hormonal therapy (also known as endocrine therapy) used to treat advanced or metastatic breast cancer that is hormone receptor-positive.

Fulvestrant is part of a class of medicines called selective estrogen receptor degraders (SERDs). These medicines stop estrogen from helping breast cancer cells to grow.

Fulvestrant was the first SERD to be approved by the Food and Drug Administration as a treatment for breast cancer.

How fulvestrant works

Fulvestrant attaches to the estrogen receptors on hormone receptor-positive breast cancer cells. This blocks estrogen's ability to attach to the estrogen receptor and can stop cancer cells from growing.

Fulvestrant is often referred to as a selective estrogen receptor degrader (SERD), which means fulvestrant can break down or weaken the estrogen receptor, making it inactive. Fulvestrant was first approved by the FDA in 2002.

In 2023, the FDA approved another SERD called elacestrant (Orserdu) for metastatic breast cancer. While fulvestrant is given by injection, elacestrant is a pill taken by mouth. To be eligible for elacestrant, the breast cancer must test positive for a mutation in a gene called ESR1.

Who gets fulvestrant

Fulvestrant can be given to adults with hormone receptor-positive advanced or metastatic breast cancer.

Fulvestrant and menopausal status

Fulvestrant is FDA approved for use in postmenopausal women with advanced or metastatic hormone receptor-positive breast cancer. Women taking fulvestrant may have gone through menopause naturally or because they chose to have their ovaries removed to reduce ovarian and breast cancer risk.

Fulvestrant can also be given to premenopausal women with advanced or metastatic hormone receptor-positive breast cancer who are taking medicines that stop the ovaries from producing estrogen. These medicines are called gonadotropin-releasing hormone (GnRH) agonists (also may be referred to as luteinizing hormone-releasing hormone agonists).

Fulvestrant in hormone receptor-positive, HER2-negative breast cancer

For women with hormone receptor-positive advanced or metastatic breast cancer that is also HER2-negative, fulvestrant can be used:

• If the cancer returns while taking an aromatase inhibitor for early stage breast cancer. In this situation, fulvestrant would commonly be given with a targeted therapy called a CDK4/6 inhibitor.
• If the cancer progresses (keeps growing) after receiving another type of hormonal therapy. The most common time fulvestrant would be given would be after cancer grows while taking an aromatase inhibitor and CDK4/6 inhibitor. Fulvestrant may be given alone or in combination with other targeted therapies.

The FDA-approved CDK 4/6 inhibitors are:

• Abemaciclib (Verzenio)
• Ribociclib (Kisqali)
• Palbociclib (Ibrance)

Fulvestrant also may be used to treat hormone receptor-positive, HER2-negative advanced or metastatic breast cancers found to have mutations in genes such as PIK3CA, AKT1, or PTEN. Biomarker testing can confirm each of these mutations. Depending on the mutation, fulvestrant can be given along with targeted treatments such as:

• Inavolisib (Itovebi) and palbociclib
• Alpelisib (Piqray)
• Capivasertib (Truqap)

Fulvestrant in hormone receptor-positive, HER2-positive breast cancer

For women with hormone receptor-positive breast cancer that is HER2-positive, fulvestrant can be used along with trastuzumab (Herceptin), a HER2-targeted therapy. Some people may take abemaciclib as well.

Fulvestrant in male breast cancer

Men with advanced or metastatic hormone receptor-positive, HER2-negative breast cancer are also eligible for treatment with fulvestrant.

How fulvestrant is given

Fulvestrant is given by injection into the buttocks. For the first month, you will receive two injections every 2 weeks at your doctor’s office. After the first month, fulvestrant is given as two injections every 4 weeks.

The standard fulvestrant dose is 500 milligrams (mg). For people with liver problems, the dose may be lowered to 250 mg per treatment. That’s because the liver breaks down fulvestrant.

Side effects and things to remember

Common side effects of fulvestrant are:

• Pain at the site you receive the injection
• Hot flashes, a common symptom of menopause
• Nausea and vomiting
• Fatigue
• Muscle, bone, and joint pain
• Headache
• Loss of appetite
• Weakness
• Cough
• Constipation
• Shortness of breath
• Higher liver enzymes, which means damage or inflammation of the liver

Fulvestrant can harm an unborn baby. You should not take fulvestrant if you’re pregnant. You also shouldn't get pregnant while taking it and for a year after treatment ends.

Women should avoid breastfeeding while taking fulvestrant.

Tell your healthcare team if you:

• Have liver problems
• Have low levels of platelets in your blood
• Bleed easily (fulvestrant is given by injection into the muscle, so your team should be aware of any bleeding issues)