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Here’s what you need to know about fulvestrant, also known as Faslodex - a hormone therapy that can be used to treat breast cancer that has spread in post-menopausal women.

1. What is fulvestrant?

Fulvestrant is a type of hormone therapy. Its generic (non-branded name) is fulvestrant. You may hear it called Faslodex, its brand name.

2. How does fulvestrant work?

Some breast cancers use oestrogen in the body to help them to grow. These are known as oestrogen receptor positive or ER-positive breast cancers.

Hormone therapies block or stop the effect of oestrogen on breast cancer cells. Different hormone therapy drugs do this in different ways.

Oestrogen receptors are usually tested on primary breast cancers using tissue from a or after surgery. If you have secondary breast cancer your treatment team may discuss taking a sample of tissue from the site of the to retest the hormone receptors. This will depend on your individual situation.

3. Who might be offered fulvestrant?

Fulvestrant is used to treat women who have gone through the menopause (are postmenopausal) who have:

  • Locally advanced breast cancer – breast cancer that has spread to the tissues and lymph nodes (glands) around the chest, neck and under the breastbone (when surgery is not possible). Sometimes breast cancer is locally advanced when it is first diagnosed. This may also happen when breast cancer comes back after treatment and may be referred to as regional recurrence
  • Secondary (metastatic) breast cancer – breast cancer that has spread to other parts of the body

Fulvestrant may be prescribed if breast cancer has progressed while you are taking, or after you have had, other hormone therapies – such as letrozole or tamoxifen. It can still work after other hormone therapies have stopped working because it acts in a different way.  

Occasionally it may be prescribed for women who haven’t been through the menopause (premenopausal) in combination with other drugs, including a drug to stop the production of hormones in the ovaries (known as ovarian suppression). Your treatment team will discuss with you what they recommend and why.  

Fulvestrant with other anti-cancer drugs

Fulvestrant may be given with another drug called a targeted therapy, such as abemaciclib, palbociclib or ribociclib.

You may be offered this if:

  • You have had hormone therapy for locally advanced or secondary breast cancer
  • Your breast cancer has not responded to treatment, or has come back, while taking hormone therapy for primary breast cancer

4. How is fulvestrant given?

Fulvestrant is given by two injections, one in each buttock. These are known as intramuscular (IM) injections.

You may be asked to hold the fulvestrant to warm it up before you have the injections. This is to reduce discomfort when it is given.

Each injection takes one to two minutes as fulvestrant is oily and needs to be given slowly.

It’s usually given at hospital every two weeks for the first three doses, then once a month.

You will usually be given fulvestrant for as long as it keeps your breast cancer under control and any side effects can be managed.

5. What are the possible side effects of fulvestrant?

Most people having fulvestrant have mild side effects that improve over time. However, everyone reacts differently. and some people may experience more side effects than others. The main side effects are listed here. You may have some or none of these. Tell you treatment team about any side effects, whether or not they are mentioned here.

Common side effects

The most common side effects that people have when taking fulvestrant are menopausal symptoms.

You may also experience:

  • Temporary pain and inflammation around the injection site
  • Feeling sick (nausea)
  • Bone or joint pain
  • Skin rashes

Fulvestrant can cause changes in your liver. This doesn’t usually cause any symptoms but you will have regular blood tests to check if your liver is working properly.

Less common side effects

Less common side effects include:

  • Loss of appetite
  • Being sick (vomiting)
  • Diarrhoea
  • General weakness or lack of energy
  • Urine infections
  • Constipation
  • Headaches

Fulvestrant can reduce the number of platelets, which help the blood to clot. This may mean you bruise or bleed more easily. Tell your treatment team if this happens.

Rare side effects of fulvestrant include vaginal discharge or vaginal bleeding. This may occur in the first few weeks of treatment, usually after changing from another hormone therapy to fulvestrant. If you have vaginal bleeding at any time, tell your treatment team.

6. Other important information

Blood clots

People with breast cancer have a higher risk of blood clots. Their risk is higher because of the cancer itself and some treatments for breast cancer. If the cancer has spread to other parts of the body (secondary breast cancer), this also increases the risk.

Having fulvestrant increases the risk of blood clots such as a deep vein thrombosis (DVT).

People with a DVT are at risk of developing a pulmonary embolism. This is when part of the blood clot breaks away and travels to the lung. Blood clots can be harmful but are treatable so it’s important to report symptoms as soon as possible.

Blood clot symptoms

If you have any of the following symptoms, contact your treatment team or go to your local A&E department immediately:

  • Pain, redness/discolouration, heat and swelling of the arm or leg
  • Swelling, redness or tenderness where a central line is inserted to give chemotherapy - for example in the arm, chest area or up into the neck
  • Shortness of breath
  • Pain or tightness in the chest
  • Unexplained cough or coughing up blood

Find out more about blood clots.

Can I take fulvestrant with other drugs?

If you’re taking any other prescribed or over-the-counter medicines, let your treatment team know.

As fulvestrant is given by injection, you need to tell your treatment team if you’re taking any blood-thinning drugs.

Talk to your treatment team or pharmacist about any complementary therapies, herbal remedies or supplements you want to use before you start using them.

7. Further support

Being diagnosed with breast cancer can make you feel lonely and isolated.

If you would like any further information and support about breast cancer or just want to talk things through, you can speak to one of our nurses below.

You may also want to visit our online forum.

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Quality assurance

This information was published in May 2021. We will revise it in May 2023.

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