Medical Oncologist
Medicines
Exemestane after letrozole or anastrozole: why switch?
Letrozole, anastrozole and exemestane are all aromatase inhibitors, yet some women are moved from one to another. This page explains the usual reasons, from joint pain and rash to cancer growth in advanced disease, how exemestane differs, what a switch involves day to day, and what it realistically can and cannot change for you.
NG
Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed September 2026, next review due September 2027
On this page
- Why would someone move from letrozole or anastrozole to exemestane?
- Four situations where a switch is discussed
- How exemestane compares with letrozole and anastrozole
- The vocabulary, in plain language
- What a switch can and cannot do
- What usually happens when you switch
- Switching when the cancer has grown
- Myths about switching to exemestane
- Common questions about switching to exemestane
The short answer
Why would someone move from letrozole or anastrozole to exemestane?
Letrozole, anastrozole and exemestane all belong to the same family of hormone tablets, called aromatase inhibitors. They are used for hormone receptor positive breast cancer in women who have been through menopause, or in younger women whose ovaries have been switched off with other treatment. All three lower the amount of oestrogen the body makes, but they do it in slightly different ways. Letrozole and anastrozole are non-steroidal and block the aromatase enzyme in a reversible way. Exemestane is steroidal, which means it is shaped like a natural hormone and switches the enzyme off permanently. The most common reason for a switch is side effects. Some women who struggle with joint pain, stiffness, rash or other problems on one tablet find another easier to live with, although this does not happen for everyone. A second reason applies to advanced breast cancer: if the cancer grows while someone is taking letrozole or anastrozole, exemestane can sometimes still help, often combined with another medicine such as everolimus. Moving to exemestane does not usually mean your first tablet failed, and it is not an upgrade to a stronger medicine. In early breast cancer, trials suggest the three tablets give broadly similar protection. The decision rests on how you are coping, the stage of your cancer and your other health needs, and it should always be made with your oncologist rather than on your own.
Side effects are the usual reason
A different tablet from the same family is sometimes better tolerated, so a switch lets you keep taking protective treatment.
Advanced cancer is a separate situation
When cancer grows on a non-steroidal tablet, exemestane may still work for a while because it acts on the enzyme differently.
It is not a stronger medicine
For early breast cancer, the three aromatase inhibitors are thought to protect against recurrence to a similar degree.
This page gives general information only. Your oncology team can advise on your own treatment.Reasons for a change
Four situations where a switch is discussed
Each one leads to a different conversation with your team.
Joint pain or stiffness
Aching joints are one of the main reasons women stop hormone tablets early. Trying exemestane is one way to stay on treatment when other measures have not helped enough.
Rash or a reaction to the tablet
Occasionally a skin rash, itching or another reaction points to one particular medicine or its ingredients. A different tablet may avoid the problem.
Cancer growth in advanced disease
If scans show the cancer has grown on letrozole or anastrozole, exemestane is one of several options, often paired with everolimus.
Fulvestrant and other targeted medicines may also be considered.A planned change in sequence
Some treatment plans move between hormone tablets on purpose, for example from tamoxifen to an aromatase inhibitor after two or three years.
Things to share before any switch
- Which symptoms you have and how long they have lasted
- Any tablets, creams or supplements you take
- Whether you have missed doses because of side effects
Side by side
How exemestane compares with letrozole and anastrozole
Question
What is generally true
How does it block oestrogen?
Exemestane switches the enzyme off permanently; the other two block it reversibly
How is it taken?
One tablet a day, and exemestane is best taken after a meal
Does it protect as well in early cancer?
Trials suggest broadly similar protection across the three tablets
Are side effects different?
The pattern is similar, but individual women sometimes tolerate one better than another
Can it work after the others in advanced cancer?
Sometimes, because resistance to one type does not always mean resistance to the other
Words you may hear
The vocabulary, in plain language
- Aromatase inhibitor
- A hormone tablet that stops the body turning other hormones into oestrogen after menopause.
- Non-steroidal
- Describes letrozole and anastrozole, which block the aromatase enzyme but can let go of it.
- Steroidal
- Describes exemestane, which is shaped like a natural hormone and disables the enzyme for good.
- Cross-resistance
- When cancer that stops responding to one medicine also stops responding to a similar one.
- Adjuvant treatment
- Treatment after surgery to lower the chance of the cancer coming back.
- Everolimus
- A targeted tablet sometimes combined with exemestane for advanced hormone receptor positive cancer.
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Being straight with you
What a switch can and cannot do
Switching is a sensible step for many women, but it helps to go in with realistic expectations.
Joint pain may not go away
Some women feel much better on exemestane, while others find their aches continue, because the underlying cause is low oestrogen, which all three tablets share. If that happens, your team can talk about tamoxifen, exercise programmes, pain relief or other approaches.
New side effects are possible
A few women notice different effects on exemestane, such as oily skin, acne or mild hair thinning.
What this page cannot tell you
It cannot tell you whether a switch is right for your cancer, your bones or your other medicines. Only your oncologist, who knows your full history, can weigh that.
In practice
What usually happens when you switch
A switch between aromatase inhibitors is normally simple, but the details should come from your own team.
Starting the new tablet
In most cases, you stop the old tablet and start exemestane the next day, with no gap needed. Sometimes a doctor suggests a short break first to see whether symptoms settle, which helps show whether the tablet is the cause. Only take a break if your team has planned it.
Your treatment time usually carries on
Time already spent on letrozole or anastrozole normally counts towards your total length of hormone therapy. A switch does not usually restart the clock, but ask your oncologist how long you will take exemestane.
Giving it a fair trial
Side effects can take several weeks to settle or change. Keep a simple diary of pain, sleep and energy so you and your team can judge how the new tablet suits you.
Advanced breast cancer
Switching when the cancer has grown
For secondary breast cancer, a change of hormone treatment is made because tests show the current treatment is no longer controlling the cancer.
Why exemestane may still help
Because exemestane disables the enzyme in a different way, some cancers that have grown on letrozole or anastrozole still respond to it for a period.
It is often combined
Exemestane is frequently given with everolimus, which targets a pathway cancer cells use to get around hormone treatment. This combination brings its own side effects, such as mouth sores, which need close monitoring.
Other choices exist
Fulvestrant, medicines targeting CDK4 and CDK6, and treatments matched to gene changes such as PIK3CA or ESR1 may suit some women better. Your team will explain why they recommend a particular option.
Commonly believed
Myths about switching to exemestane
A switch means my cancer has come back.
In early breast cancer, switches are usually made because of side effects, not because the cancer has returned.
Exemestane is the strongest of the three.
Research suggests the three aromatase inhibitors offer broadly similar protection in early breast cancer.
I can switch tablets myself if I have leftovers.
Never swap or combine hormone tablets without your oncologist, as doses and plans need checking.
If exemestane also causes pain, I have run out of options.
Tamoxifen, exercise, pain relief and other approaches can still be explored with your team.
Questions we are asked
Common questions about switching to exemestane
Will switching to exemestane lower my protection against cancer returning?
For early breast cancer, current evidence suggests exemestane protects about as well as letrozole and anastrozole. The bigger risk to your protection is stopping hormone therapy altogether because of side effects. A switch that helps you keep taking a tablet every day is usually a positive step.
How soon will I know if exemestane suits me better?
Many women can tell within one to three months whether their symptoms have eased. Joint aches sometimes take longer to settle. Keep a note of how you feel each week and share it at your next review, so your team can decide whether to continue or look at other options.
Do I need a gap between my old tablet and exemestane?
Usually not. Most women start exemestane the day after their last letrozole or anastrozole tablet. Occasionally a doctor suggests a short, planned break to check whether symptoms are caused by the medicine. Do not take a break on your own, because the protection depends on steady daily treatment.
Can I go back to letrozole or anastrozole later?
Sometimes, yes. If exemestane causes new problems, your oncologist may suggest returning to your earlier tablet, trying the other non-steroidal one, or moving to tamoxifen. The aim is to find a treatment you can keep taking for the planned length of time.
Is exemestane taken differently from my old tablet?
It is also one tablet a day, but exemestane is absorbed better when taken after a meal. Many women take it after breakfast or dinner at the same time each day. Letrozole and anastrozole can be taken with or without food, so this is a small but useful change to your routine.
Will my bones be affected differently on exemestane?
All aromatase inhibitors can thin the bones, including exemestane. Some early research suggested a gentler effect, but this is not certain. Keep up bone density checks, calcium and vitamin D as advised, and weight-bearing exercise such as walking.
I am premenopausal. Can I switch to exemestane?
Only if your ovaries are also switched off with injections or surgery. Before menopause, the ovaries make most of your oestrogen, and exemestane on its own cannot block that. In fact, it can stimulate the ovaries. Your oncologist will check your menopausal status before any switch.
Should I switch if I feel fine on my current tablet?
In early breast cancer, there is usually no reason to switch between aromatase inhibitors if you are coping well. A change is normally considered for side effects, a reaction to the tablet or, in advanced cancer, signs of growth. Ask your team if you have heard otherwise.
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Sources
- Cancer Research UK — Exemestane (Aromasin)
- Macmillan Cancer Support — Exemestane
- National Cancer Institute — Hormone Therapy for Breast Cancer
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.