Medical Oncologist
Medicines
How much does letrozole actually help? The numbers explained
Letrozole lowers the chance of hormone-receptor-positive breast cancer coming back, and the protection lasts beyond the years you take it. How much it helps you depends on your starting risk. This page explains relative and absolute benefit, how tools estimate personal gain, and how to weigh benefit against side effects.
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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
- How much does letrozole actually lower the risk of breast cancer returning?
- Four things letrozole helps reduce
- Relative and absolute benefit, in plain terms
- The vocabulary, in plain language
- What the numbers cannot do
- A made-up example of how starting risk changes the gain
- Weighing benefit against side effects
- Questions to ask about your own benefit
- What people assume about letrozole's benefit
- Common questions about letrozole's benefit
The short answer
How much does letrozole actually lower the risk of breast cancer returning?
Letrozole lowers the chance of hormone-receptor-positive breast cancer coming back, but how much it helps you personally depends on how high your risk was to begin with. Large combined analyses of many trials, involving tens of thousands of women, show that around five years of hormone therapy substantially reduces the risk of recurrence and of dying from breast cancer, with the protection lasting well beyond the years the tablets are taken. For women after menopause, aromatase inhibitors such as letrozole lower the risk of recurrence somewhat more than tamoxifen does. The key idea to understand is the difference between relative and absolute benefit. A relative benefit describes the proportion of risk removed, such as a treatment cutting risk by a third. An absolute benefit tells you how many women out of a hundred actually avoid a recurrence. The same relative cut makes a big absolute difference when the starting risk is high, for example with a large tumour or cancer in several lymph nodes, and a smaller absolute difference when the starting risk is low, such as with a small, node-negative, low-grade tumour. This is why two women on the same tablet can gain very different amounts. Online tools such as Predict Breast, used in many clinics, combine your age, tumour size, grade, lymph nodes and receptor status to estimate the benefit of each treatment for someone like you. Your oncologist can go through these estimates with you and explain what they mean.
The benefit is real and lasting
Hormone therapy reduces recurrence and the effect continues after the tablets stop.
Your starting risk shapes your gain
Higher-risk cancers gain more in absolute terms from the same tablet.
Ask for your personal numbers
Your oncologist can estimate your likely benefit using your own cancer details.
This page gives general information only and does not estimate your own benefit. Your oncologist can.What it protects against
Four things letrozole helps reduce
The benefit shows up in several ways, not only one.
Local return
Cancer coming back in the same breast, chest wall or nearby lymph nodes.
Distant spread
Cancer reappearing in bones, liver, lungs or elsewhere, which is the most important outcome to prevent.
This is the main driver of survival.A new cancer in the other breast
Hormone therapy lowers the chance of a new hormone-positive cancer in the opposite breast.
Death from breast cancer
By preventing recurrence, hormone therapy lowers the risk of dying from breast cancer over the long term.
Benefit is larger when
- The tumour was large or high grade
- Lymph nodes were involved
- The tablets are taken steadily
Reading the numbers
Relative and absolute benefit, in plain terms
Term
What it means for you
Relative benefit
The share of risk a treatment removes
Absolute benefit
How many out of a hundred women avoid recurrence because of it
High starting risk
Larger absolute gain from the same tablet
Low starting risk
Smaller absolute gain, though still a real benefit
Personal estimate
Worked out from your age and cancer details with your doctor
Words you will hear
The vocabulary, in plain language
- Recurrence
- Breast cancer that comes back after treatment, nearby or elsewhere in the body.
- Relative risk reduction
- The proportion by which a treatment lowers risk compared with not having it.
- Absolute risk reduction
- The actual difference in the number of people affected, often shown out of a hundred.
- Meta-analysis
- A study that combines results from many trials to give a clearer answer.
- Predict Breast
- A free online tool clinicians use to estimate the benefit of treatments after surgery.
- Carry-over effect
- Protection from hormone therapy that continues after the tablets are stopped.
Being straight with you
What the numbers cannot do
Estimates are useful, but they describe groups of women, not certainties for one person.
No one can say whether it helped you
If your cancer never returns, there is no way to know whether letrozole prevented it or it would not have returned anyway.
Tools have limits
Prediction tools are based mostly on data from Western populations and may be less exact for women in India.
Benefit needs regular use
Trial results come from women who largely took their tablets. Frequent missed doses or stopping early reduce the gain.
What this page cannot tell you
It cannot give your personal benefit. Your oncologist can estimate it with you.
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An illustration
A made-up example of how starting risk changes the gain
This example uses round, invented numbers only to show the arithmetic. It is not data about letrozole.
A higher-risk situation
Imagine a group where thirty women out of a hundred would have a recurrence without hormone therapy. If a treatment removed a third of that risk, about ten of those women would be spared.
A lower-risk situation
Now imagine a group where six out of a hundred would have a recurrence. Removing a third of that risk would spare about two women.
What this shows
The treatment works the same way in both groups, but the number of women who gain depends heavily on the starting risk.
Making sense of it
Weighing benefit against side effects
Understanding your benefit can help if side effects make you question treatment.
When benefit is larger
It is usually worth working hard to manage side effects, switching tablets if needed, to stay on treatment.
When benefit is smaller
Some women, with their oncologist, decide that a shorter course or a different tablet is a reasonable balance.
Talk before deciding
Your oncologist can show your estimate and discuss options openly.
At your appointment
Questions to ask about your own benefit
A few clear questions can turn general statistics into something meaningful for you.
Useful questions
Ask what your risk of recurrence would be without hormone therapy, how much letrozole is likely to lower it in absolute terms, and how extending treatment beyond five years would change that estimate.
Ask for it in writing
Some clinics can print the estimate or draw a simple picture, which makes it easier to share with family and think about at home.
Commonly believed
What people assume about letrozole's benefit
If my cancer was small, letrozole does nothing.
The absolute gain may be smaller, but it still lowers risk.
A one-third reduction means a one-third chance of recurrence.
Relative reductions describe how much risk is removed, not your remaining risk.
Benefit stops the day I stop the tablet.
Protection continues for years after a completed course.
Online calculators give exact answers.
They give estimates for similar groups and need a doctor's interpretation.
Questions we are asked
Common questions about letrozole's benefit
Is letrozole better than tamoxifen?
For women after menopause, combined trial results show aromatase inhibitors lower recurrence somewhat more than tamoxifen. The difference is moderate. Tamoxifen remains a good option when an aromatase inhibitor is not suitable or not tolerated, and for women before menopause.
Can my doctor give me my personal numbers?
Often, yes. Using your pathology report, your oncologist can estimate the likely benefit of hormone therapy with tools such as Predict Breast. Ask them to explain the results in absolute terms, out of a hundred women like you.
Does letrozole help if I also had chemotherapy?
Yes. Chemotherapy and hormone therapy work in different ways, and their benefits add together for hormone-receptor-positive cancers. Having had chemotherapy does not make letrozole unnecessary.
How long does the protection last?
Studies show the reduction in recurrence continues for years after about five years of hormone therapy is completed. Late recurrences can still happen, which is why some women are offered extended treatment.
What does letrozole do in advanced cancer?
In advanced breast cancer, letrozole aims to control the cancer and delay its growth for as long as possible, often combined with a CDK4/6 inhibitor. The benefit is measured in time the cancer is held back rather than prevention of return.
Does taking it for ten years double the benefit?
No. The extra years add a smaller further benefit than the first five. For higher-risk cancers this may be worthwhile, while for lower-risk cancers side effects may outweigh it. Your oncologist can help you weigh this.
Why are the numbers presented so differently in different places?
Some sources quote relative reductions, which sound large, and others absolute ones, which sound smaller. Both can be accurate. Asking which type of number you are looking at avoids confusion.
Does my ethnicity change the benefit?
Hormone therapy works through the same biology in all women. Estimates from tools may be less precise for Indian women because of the data they were built on, so your oncologist's judgement remains important.
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Speak to a breast cancer specialist
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Sources
- The Lancet — Aromatase inhibitors versus tamoxifen in early breast cancer: patient-level meta-analysis of the randomised trials
- University of Cambridge — Predict Breast
- 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.