An aromatase inhibitor for breast cancer
Letrozole
An aromatase inhibitor that lowers oestrogen, used for hormone-receptor-positive breast cancer after the menopause.
What is Letrozole?
Letrozole 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, and is sometimes used in fertility treatment under specialist care.
Education and reference only. This is a plain-language guide to Letrozole — 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
Letrozole 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, to reduce the chance of the cancer returning or to control advanced disease. It is only suitable after the menopause. It is also used in some specialist fertility settings, but that is a separate, supervised use.
How it works
After the menopause, the body makes small amounts of oestrogen by converting other hormones using the enzyme aromatase. Many breast cancers are fuelled by oestrogen and grow faster when it is present. Letrozole blocks aromatase, greatly reducing the amount of oestrogen in the body. With less oestrogen, hormone-sensitive breast cancer cells lose the signal that drives their growth.
Company & origin
Originated / developed by: Originally developed by Novartis and now widely available as a generic medicine..
An aromatase inhibitor introduced in the late 1990s for hormone-receptor-positive breast cancer in postmenopausal women.
Practical use
How to take Letrozole
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take one tablet once a day, ideally at about the same time, with or without food.
- Swallow the tablet whole with a drink of water.
- Keep taking it for the full course your team advises, often several years, even when you feel well.
- Report troublesome joint pain, hot flushes or low mood, as your team can help.
- If you miss a dose, take it when you remember unless the next dose is close, then skip it — never double up.
Weighing it up
Advantages & disadvantages of Letrozole
Advantages
- Reduces the risk of hormone-sensitive breast cancer returning after the menopause.
- Taken as a simple once-a-day tablet and available as a generic medicine.
- Does not carry the small risk of womb cancer or blood clots seen with tamoxifen.
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, vaginal dryness and reduced sex drive.
Practical use
Good to know
Letrozole is taken once a day, usually for several years, to lower the chance of breast cancer returning. Because it works by reducing oestrogen, it is only used after the menopause. Joint and muscle aches, hot flushes and tiredness are common, and lower oestrogen can weaken bones, so bone strength is monitored. It is important to keep taking it as prescribed, as the benefit builds 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 (outside specialist fertility use).
- Women who are pregnant or breastfeeding.
- Anyone who has had a serious allergic reaction to letrozole.
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 tiredness.
- Vaginal dryness, reduced sex drive, headache 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.
- Tamoxifen can reduce its effect, so the two are not normally combined.
- Tell your team about all medicines and supplements you take, including over-the-counter products.
Available as: Tablets.
Answers
Letrozole: frequently asked questions
Why is letrozole only used after the menopause?
Before the menopause, the ovaries produce large amounts of oestrogen that letrozole cannot control. After the menopause, oestrogen comes mainly from the aromatase enzyme in other tissues, which letrozole blocks. Women who have not reached the menopause are usually given other treatments, such as tamoxifen.
What is the difference between letrozole and anastrozole?
Both are aromatase inhibitors that lower oestrogen to treat hormone-sensitive breast cancer after the menopause, and they work in very similar ways. The choice between them depends on your situation and how well you tolerate each. Your team will recommend the most suitable one for you.
Will letrozole weaken 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 check your bone density and may advise calcium, vitamin D, weight-bearing exercise or bone-protecting medicine to reduce the risk of fractures.
How should I manage hot flushes and joint pain?
Hot flushes and joint or muscle aches are common with letrozole. Keeping active, dressing in layers, and using painkillers your team recommends can help. If symptoms are severe or affect daily life, tell your team rather than stopping the tablets on your own.
How long will I take letrozole?
It is usually taken for several years, as the protection against the cancer returning builds over time. Your team will advise how long is right for you and may sometimes switch you between hormone treatments. Keep taking it as prescribed even when you feel well.
The wider class
About Aromatase inhibitors
Letrozole 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: Letrozole.
- electronic Medicines Compendium (SmPC): Femara (letrozole).
- NICE CKS: Letrozole.
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