This expert review looked at the benefits and possible harms of breast screening.
The UK breast screening programme
Screening means looking for early signs of a particular disease in healthy people who don’t have any symptoms. Screening for cancer aims to find cancers as early as possible when the chance of cure is highest. Breast screening means using tests to find breast cancers as early as possible, before they cause symptoms such as a lump in the breast.
The UK breast screening programme uses mammograms to screen for breast cancer in women every 3 years between the ages of 50 and 70. A mammogram is a specialised x-ray of the breast.
After a mammogram, women who have signs of something unusual are called back for more tests. These might include scans or a biopsy to confirm or rule out breast cancer.
If a diagnosis is confirmed, women are offered breast cancer treatment.
Out of all the women who have breast cancer found through screening:
- more than 99 out of every 100 (99%) have surgery
- about 87 out of every 100 (87%) have hormone therapy
- 80 out of every 100 (80%) have radiotherapy
- about 26 out of every 100 (26%) have chemotherapy
Background to the screening programme
The NHS Breast Screening Programme was the first of its kind in the world. It began inviting women for screening in 1988 and covered the whole of the UK by the mid 1990s.
In England the programme is currently being expanded and will offer mammograms to all women between 47 and 73 years old. If you are older than the screening age, you can ask to have a mammogram every 3 years by contacting your local breast screening unit.
Why the review was carried out
The breast screening review was set up after concerns were raised that women were being told a lot about the possible benefit and not enough about the possible harm. With different experts speaking out both in favour and against breast screening, a public review was needed to help get the true picture. The UK Government and Cancer Research UK asked a world renowned statistician, Professor Sir Michael Marmot, to chair an independent Panel to review the evidence.
The aim of the review was to have a group of independent experts weigh up all the evidence about the pros and cons of breast screening. Then it would be possible to make sure that women had the clearest information possible, to help them decide whether to have breast screening or not.
The review panel
The panel included a breast cancer patient experienced in representing the needs of cancer patients, and experts in medical statistics, research, and breast cancer treatment.
Known benefits of screening
The benefit of breast screening is that some women will have a breast cancer found at the earliest possible stage, before it has caused any symptoms. Many cancers found during screening would have been found later if women hadn’t been screened. Some will be successfully treated and others unfortunately won’t. But the screening programme does mean that more cancers are successfully treated than if we didn’t have screening.
Known downsides to screening
The possible harms from breast screening are:
- diagnosing slow growing breast cancers that would never have caused any harm (overdiagnosis)
- exposure to small amounts of radiation during screening
- unnecessary anxiety, including for women called back for more tests, but found not to have cancer
Overdiagnosis was the main issue that the Panel considered and is a major problem. Some breast cancers found through screening would never have become life threatening. But currently doctors can’t tell whether a breast cancer found during screening is life threatening or not.
Women who have breast cancers found through the screening programme are all offered treatment. This is why we talk about overdiagnosis. Some women go on to have cancer treatment that they would never have needed if they weren't screened. And of course they have the side effects and anxiety that anyone having treatment for cancer goes through. One of the main aims of the screening review panel was to try to find out how many women are overdiagnosed.
Exposure to radiation
Any risk from radiation from mammograms is likely to be very small. For every 10,000 women who have regular 3 yearly screening between 47 and 73 years old, experts estimate that there will be between 3 and 6 extra breast cancers caused by radiation.
In the screening programme, far more women are called back for tests who turn out to be fine than who actually have breast cancer.
At the time of the review, only about 1 in 25 women were called back and about 1 in 5 of those had breast cancer. So, 4 out of 5 women called back didn't have breast cancer. Of course, women are very anxious that they might have cancer when they are called back.
Information the review looked at
The panel looked at all the existing research on breast screening that was relevant to the UK Breast Screening Programme. This included randomised controlled trials and observational studies.
A randomised trial puts people into groups at random and, for example, half are screened and half not. The researchers then follow the groups to see what happens to them.
An observational study collects data on what happens to people who either take part in screening or don’t. These people may have made the choice themselves. Or some women may have access to screening and others don't if they live in countries that have different policies about screening.
All the randomised trials were set up at least 20 to 30 years ago. The observational studies were more recent.
What the review found
This video gives information about the findings of the breast cancer screening review.
Voiceover: Millions of British women between the ages of 50 and 70 are regularly invited for mammograms by the NHS, ever since research first showed breast screening saves lives.
But over the years some scientists have questioned the extent to which this is true and whether the pros of breast screening outweigh the cons.
To find out what’s going on Cancer Research UK and the department of health commissioned an independent panel of experts to examine the evidence and help answer three key questions.
Sara Hiom (Director of Information, Cancer Research UK): The first of course is how many breast cancer deaths can be prevented by the screening programmes in this country. What is the level of harm if you like, and we’re mainly talking about over diagnosis here. And also how does the balance, of the benefits and the harms pan out for women.
Voiceover: The panel examined all the evidence on breast screening. They decided the best quality data came from several large breast screening trials carried out over the last 40 years.
When they put all of the numbers together the evidence suggested that screening reduces breast cancer deaths by around 20%. So the panel’s best estimates are that if there were no screening 21 out of every thousand women would die of breast cancer.
But among women who go for screening that figure drops to 16 out of every 1000 women. That’s 5 lives saved. So what does that mean for women in the UK?
Sara: So the good news is that the panel have estimated that the number of breast cancer deaths that are prevented through the NHS screening programmes is 1300 in the UK each year. So that’s some sizable number of breast cancer deaths prevented each year in the UK.
On the downside however, the panel did find that over diagnosis does indeed exist. Over diagnosis is best described as those cancers that are detected and treated through the screening programme that would not have otherwise gone on to cause the woman a problem during her lifetime.
Voiceover: In a perfect world where screening only identified cancers that definitely needed treatment the same number of women would ultimately be diagnosed with cancer whether they’d been screened or not. Screening just spots cancers earlier.
In reality the panel showed that there were more cases of cancer detected among screened women than those who weren’t screened. Using the trial data the panel estimated that for every 1000 women who go for screening, 17 extra women are diagnosed with breast cancer. These cancers are said to be over diagnosed.
Sara: The important thing here to remember is that for any woman going through the screening programme if they’re found to have a cancer as detected on a mammogram, there is no way for them or their doctors to know whether that cancer that has been picked up through the screening programme will cause them a problem in their lifetime or not. And that is why every woman that has a cancer diagnosed in this way will be offered treatment.
Voiceover: Across the UK those extra cancers add up to about 4000 women being treated every year for cancer that would not have caused a problem in their lifetime.
This compares with 1300 women whose lives are saved by screening. That’s one life saved for three cancers over diagnosed.
So do the pros of breast screening outweigh the cons?
Prof Peter Johnson (Chief Clinician, Cancer Research UK): On balance then we still that the breast cancer screening programme is a good idea and would very much encourage women who are invited to come for screening to do that.
What’s obviously very important from this is that if a tumour is picked up and if you are thinking about having treatment you have a careful discussion with the team looking after you about what that might involve.
Voiceover: Meanwhile, doctors and researchers are working to find a reliable way to define different types of breast cancer and determine whether a woman needs treatment or not.
Dr Harpal Kumar (Chief Executive, Cancer Research UK): There are a number of ways in which we hope to be able to improve the breast screening programme in the future through further research. So for example we’re currently looking at whether we ought to extend screening into the 70’s.
We’re also thinking about ways in which we might be able to determine which women are most at risk of developing breast cancer and perhaps targeting screening at them from a younger age.
Moreover what we ought to be able to do in the future is develop better tests that enable us to distinguish those cancers which really need treating from those which perhaps we might not treat at least at the initial stages and we’re testing a number of possibilities in that regard now and we hope we’ll have those tests available to us in the future.
Voiceover: For more information go to our website to find a fact sheet including some easy to understand statistics.
It is important to put the findings of the breast screening review in context with the breast screening programme as a whole.
In the year from April 2009 to March 2010, 1,998,225 women between 50 and 70 years old had breast screening in the UK. 15,517 of these women had cancer diagnosed.
The Panel found that overall in the UK, having breast screening means that about 1,300 breast cancer deaths are prevented each year. These are cancers that are found and treated earlier than they would have been if we didn’t have a screening programme.
But also, out of the total of around 15,500 women diagnosed with breast cancer through screening at that time, 4,000 of them were overdiagnosed. So around 1 in 4 of women diagnosed with breast cancer through screening would never have had a problem from their breast cancer if they hadn’t been screened.
The Panel say that there is little reliable research evidence on how many women are diagnosed with breast cancers that would not go on to cause them any problems (an overdiagnosed breast cancer). This is the best estimate they could produce, given the lack of reliable evidence.
To simplify the figures as much as possible, this means that for every breast cancer death prevented through screening, about 3 women will have treatment for a cancer that would not have caused them problems. Their doctor would not have known that at the time, or afterwards, because they can’t reliably tell which breast cancers are life threatening and which aren’t.
Thinking about the effects on the UK as a whole, the Panel’s conclusion was that the UK breast screening programme has significant benefit and should continue.
Deciding whether to have screening
The decision for any individual woman is not necessarily an easy one. That is why we have tried to set out the evidence as clearly as we can. There are two sides to it and only you can decide which is more important to you.
Cancer Research UK has worked out the following statistics to try to show the benefits and risks as clearly as we can.
Women who have screening
After 20 years, out of 1,000 women who have screening regularly over that time, about 75 will be diagnosed with breast cancer and have treatment. Out of these 75 women:
- 16 will die from breast cancer
- 59 will be successfully treated and survive their breast cancer
Women who don't have screening
Whereas, after 20 years, amongst 1,000 women who have not had screening, around 58 will be diagnosed with breast cancer. Of these 58 women:
- 21 will die from breast cancer
- 37 will be successfully treated and survive their breast cancer
So for every 1,000 women screened, about 5 lives are saved at the expense of around 17 women being diagnosed and treated for a cancer that would never have caused them any problem.
Issues to consider
You can’t know whether you will benefit from screening or end up having treatment that you might never have needed.
If you choose to have screening, you are accepting the chance of having your life extended. But you also risking being overdiagnosed and having at least surgery to remove part or all of a breast, and possibly other cancer treatment.
If you choose not to have screening, you run a slightly higher risk of dying because a breast cancer wasn’t found early enough.
Cancer Research UK recommendation
On balance, after taking all the evidence into account, Cancer Research UK recommends breast screening. But it is your choice and you need to read the information sent with the screening invitation letter to help you to make up your mind.