Oncology
Aromatase inhibitors
Anastrozole, letrozole, exemestane — Hormone treatment for breast cancer after the menopause — with attention to bone and joints.
Education and reference only. This is a plain-language class overview — it deliberately contains no doses. Always check the current Summary of Product Characteristics (SmPC), the BNF and your local formulary before prescribing or administering any medicine.
What it is
Aromatase inhibitors are hormone (endocrine) treatments for oestrogen-driven breast cancer in post-menopausal women, used after surgery to reduce recurrence and sometimes in advanced disease.
How it works
After the menopause, most of the body's oestrogen is made outside the ovaries by an enzyme called aromatase, which converts other hormones into oestrogen. These drugs block aromatase, lowering oestrogen levels and starving oestrogen-sensitive cancer of its growth signal.
In practice
In practice aromatase inhibitors are a mainstay of endocrine treatment for hormone-receptor-positive breast cancer in post-menopausal women, taken for several years to lower recurrence, and the choice between them and tamoxifen depends on menopausal status and individual risk. Because they drive oestrogen levels very low, their characteristic problems are musculoskeletal and skeletal: joint and muscle aches are common and a frequent reason for stopping (so they are actively managed to keep people on treatment), and accelerated bone loss raises fracture risk, so bone density is assessed and protected, often with calcium, vitamin D and sometimes a bone-strengthening drug. Unlike tamoxifen they do not raise the risk of clots or womb cancer, but they can worsen cholesterol and cause hot flushes and vaginal dryness. They are used only after the menopause, because they do not work against the ovaries' oestrogen production.
Examples
Practical use
How to take it & use it well
- Anastrozole, letrozole and exemestane are tablets taken by mouth, usually once a day, for post-menopausal hormone-sensitive breast cancer.
- Take at around the same time each day, with or without food, and keep taking it for the full course your specialist advises.
- These medicines lower oestrogen levels, which can affect the bones, so bone density may be checked and bone-protecting steps advised.
- Stay active, consider calcium and vitamin D as advised, and discuss bone health with your team.
- Report troublesome joint or muscle aches, as these are common and there are ways to help.
- Do not stop without discussing it with your specialist, as continuing gives the best protection.
Common uses
- Hormone-receptor-positive breast cancer in post-menopausal women
- Prevention of recurrence after surgery
- Advanced/metastatic hormone-positive breast cancer
Monitoring
- Bone density and fracture-risk protection
- Joint/muscle symptoms and adherence
- Lipids and menopausal symptoms
Weighing it up
Advantages & disadvantages
Advantages
- Reduce the risk of hormone-sensitive breast cancer returning in post-menopausal women.
- Taken as a simple once-daily tablet at home.
- Do not carry the same clot and womb-lining risks as tamoxifen.
- Can be an effective alternative for those who cannot take or have completed tamoxifen.
Disadvantages
- Can cause thinning of the bones and a higher risk of fractures.
- Joint and muscle aches and stiffness are common.
- May cause hot flushes, tiredness and mood changes.
- Only suitable for women who are post-menopausal.
- Can cause vaginal dryness and reduced sex drive for some people.
Key safety principles
What to watch for
- Accelerated bone loss and fracture risk — assess and protect bone (calcium, vitamin D, sometimes a bone-strengthening drug).
- Joint and muscle aches are common and a frequent reason for stopping — manage actively to maintain adherence.
- Used only after the menopause; can worsen cholesterol and cause hot flushes/vaginal dryness (but, unlike tamoxifen, no extra clot or womb-cancer risk).
Key interactions
What to avoid or check alongside
- Oestrogen-containing products, including some HRT and vaginal oestrogens, can counteract these medicines and are generally avoided.
- Tamoxifen taken at the same time can reduce the effect of aromatase inhibitors, so they are not normally combined.
- Medicines and supplements that affect bone health are reviewed because of the added fracture risk.
- Tell your team about all medicines and herbal products so possible interactions can be checked.
Patient & carer advice
- Joint aches are common — tell us rather than stopping, as we can help
- Look after your bones: take calcium and vitamin D as advised and keep active
- Report new or worsening bone pain
Use with
Related clinical calculators
Dose and risk decisions for this class often depend on renal function, weight or bleeding/stroke risk. These tools help:
Answers
Aromatase inhibitors: frequently asked questions
Why do these medicines affect my bones?
Aromatase inhibitors lower oestrogen, which normally helps protect bone. Lower oestrogen can lead to bone thinning and a higher fracture risk, so bone density may be monitored and bone-protecting steps advised.
Are aromatase inhibitors suitable before the menopause?
On their own they are generally used in post-menopausal women, because in younger women the ovaries can override their effect. Your specialist decides the right hormone treatment for your situation.
What can help the joint aches?
Joint and muscle aches are common. Gentle regular exercise, keeping active and simple pain relief can help, and your team may suggest other options or review the medicine if symptoms are severe.
Can I use HRT while taking an aromatase inhibitor?
Oestrogen-containing HRT can counteract these medicines and is generally avoided. If you have menopausal symptoms, discuss non-hormonal options with your team.
How long will I take an aromatase inhibitor?
These are usually taken for several years to give the best protection against the cancer returning. Your specialist will advise the exact length and review you regularly.
Authoritative sources
Always verify against the source
This overview is for orientation. For doses, interactions, contra-indications and the full monograph, use:
Related guides
Need a custom medicines or prescribing resource?
We build evidence-led clinical references, calculators and decision aids for teams.