An aromatase inhibitor for breast cancer
Exemestane
An aromatase inhibitor that lowers oestrogen, used for hormone-receptor-positive breast cancer after the menopause.
What is Exemestane?
Exemestane is an aromatase inhibitor. It lowers the amount of oestrogen in the body, which slows or stops the growth of breast cancers that depend on oestrogen. It is used in postmenopausal women with hormone-receptor-positive breast cancer, often for several years, sometimes after a period of tamoxifen.
Education and reference only. This is a plain-language guide to Exemestane — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Exemestane is an aromatase inhibitor used to treat hormone-receptor-positive breast cancer in women who have been through the menopause. It is taken as a daily tablet, often for several years, and is sometimes used after an initial period of treatment with tamoxifen. It works slightly differently from anastrozole and letrozole by permanently switching off the aromatase enzyme. It is only suitable after the menopause.
How it works
After the menopause, the body makes small amounts of oestrogen using the enzyme aromatase to convert other hormones, and many breast cancers grow faster when oestrogen is present. Exemestane binds to aromatase and inactivates it, so the body produces far less oestrogen. Unlike some other aromatase inhibitors, it disables the enzyme permanently, so new enzyme has to be made before oestrogen production recovers. With less oestrogen, hormone-sensitive cancer cells lose the signal that drives their growth.
Company & origin
Originated / developed by: Originally developed by Pfizer and now available as a generic medicine..
An aromatase inhibitor introduced in the early 2000s for hormone-receptor-positive breast cancer in postmenopausal women.
Practical use
How to take Exemestane
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take one tablet once a day, ideally after a meal, which helps it be absorbed.
- Try to take it at about the same time each day, swallowed whole with water.
- Keep taking it for the full course your team recommends, often several years, even when you feel well.
- Tell your team about troublesome joint pain, hot flushes or low mood, as there are ways to help.
- If you miss a dose, take it when you remember unless the next dose is near, then skip it — never take two together.
Weighing it up
Advantages & disadvantages of Exemestane
Advantages
- Reduces the risk of hormone-sensitive breast cancer returning after the menopause.
- Offers an alternative for women switched from tamoxifen or another aromatase inhibitor.
- Taken as a simple once-a-day tablet and available as a generic medicine.
Disadvantages
- Commonly causes joint and muscle aches and stiffness, which some women find hard to tolerate.
- Lowers oestrogen, which can weaken bones and increase the risk of osteoporosis.
- Can cause hot flushes, tiredness, sweating and reduced sex drive.
Practical use
Good to know
Exemestane is taken once a day, usually for several years, to lower the chance of breast cancer returning. It is best taken after food. Because it lowers oestrogen, it is only used after the menopause, and joint aches, hot flushes and tiredness are common. Lower oestrogen can weaken bones, so bone strength is monitored and protective steps may be advised. Keeping to the treatment as prescribed gives the best protection over time.
Who should not take it / use with caution
- Women who have not yet been through the menopause, as it does not control oestrogen made by working ovaries.
- Women who are pregnant or breastfeeding.
- Anyone who has had a serious allergic reaction to exemestane.
Monitoring
- Bone-density scans to check for thinning of the bones, with calcium and vitamin D or other treatment if needed.
- Review of joint pain, hot flushes and other side effects.
- Regular breast-cancer follow-up appointments.
Side effects
- Joint and muscle pain or stiffness, hot flushes and sweating.
- Tiredness, headache, vaginal dryness and mood changes.
- Thinning of the bones (osteoporosis) over time, with a higher risk of fractures.
Key interactions
- Medicines containing oestrogen (including some HRT) work against it and should not be taken alongside it.
- Certain medicines that strongly affect the liver (such as some anti-epileptics and the herbal remedy St John's wort) can reduce its levels.
- Tell your team about all medicines and supplements you take, including over-the-counter products.
Available as: Tablets.
Answers
Exemestane: frequently asked questions
How is exemestane different from anastrozole and letrozole?
All three are aromatase inhibitors that lower oestrogen, but exemestane permanently inactivates the aromatase enzyme, while the other two block it reversibly. In practice they are all used to treat hormone-sensitive breast cancer after the menopause, and your team will choose based on your situation and tolerance.
Should I take exemestane with food?
Yes, it is usually taken after a meal, as food helps the body absorb it. Taking it at the same time each day, after eating, makes this easy to remember. Follow the specific advice on your prescription.
Will exemestane affect my bones?
Because it reduces oestrogen, which helps keep bones strong, it can lead to thinning of the bones over time. Your team will usually monitor your bone density and may advise calcium, vitamin D, exercise or bone-protecting medicine to lower the risk of fractures.
Can I take exemestane before the menopause?
No, on its own it is only used after the menopause, because it cannot control the larger amount of oestrogen made by working ovaries. Women who have not reached the menopause are treated differently, often with tamoxifen, sometimes alongside other measures.
How long will I take exemestane?
It is usually taken for several years, as the protection against the cancer returning builds over time, and it is sometimes used after a period of tamoxifen. Your team will tell you how long is right for you, and you should keep taking it as prescribed even when you feel well.
The wider class
About Aromatase inhibitors
Exemestane belongs to the aromatase inhibitors class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF: Exemestane.
- electronic Medicines Compendium (SmPC): Aromasin (exemestane).
- NICE CKS: Exemestane.
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