Is it worth going for breast cancer screening?

The debate over breast cancer screening is not for the faint-hearted. Professor Michael Baum, an eminent cancer surgeon who helped set up the UK cancer screening programme, told me once about what happened when he spoke to an audience of women in the US about his doubts about mammography. ‘They threw chairs at me,’ he said, seemingly still baffled by the angry reaction.

So please, no chairs. It’s a complicated field and I’m going to do my best to pick my way through the recent research to give some kind of answer to the question.

The debate hotted up in the last 2 weeks with the publication of two different papers by two different research teams, looking at the impact of breast cancer screening on deaths from breast cancer. The research teams came to wildly different conclusions. The first team said screening made no difference to the numbers of women dying from breast cancer. The second said thousands of lives had been saved. How did they reach such different conclusions?

To begin with, they looked at different populations. The first team looked at what happened in Denmark, where breast cancer screening was introduced in some districts in the early 1990s, but not at all in other districts. Between 1997 and 2007, deaths from breast cancer fell by 1 percent to 2 percent, in all districts. Screening didn’t make an obvious difference. (For more on this study, see my colleague Philip Wilson’s analysis on The Guardian.)

The second study, published a week later, re-analysed data from two studies, one from Sweden and one from UK. I’m going to focus on the UK study. Because breast cancer screening began simultaneously across the UK, there was no way to compare screened with unscreened populations. Instead, the researchers looked at deaths from breast cancer before and after the introduction of screening. They used a complex formula to calculate the number of fatal cancers they’d expect to see, compared to the numbers that actually happened, since the introduction of screening. They calculated that 5.7 deaths from cancer were prevented for every 1000 women screened, in the 20 years since screening began.

So it is possible that British women were more at risk of getting cancer than Danish women, and that screening saved many of these women from dying. Or its possible that the statistical team made some incorrect assumptions about how many cancer deaths we would have seen in the UK, had screening not been introduced.

Certainly and happily, deaths from breast cancer have fallen fast in the UK, although the numbers actually being diagnosed have increased 6% in the last 10 years, according to Cancer Research UK. Could this be the key? Prof Baum has said he believes the fall in the numbers of deaths is to do with improved treatment, not screening. Screening means more people are being diagnosed, but the fall in deaths is down to better surgical techniques and better drugs.

The idea of screening is to catch cancers early, while they are easy to treat and before they spread. Mammography, which uses x-rays to take a picture of the breast, can reveal lumps to small to feel or notice. The big question is, would these little lumps have grown? Most screening experts now admit that mammography leads to a certain amount of over-diagnosis, where small abnormalities are picked up by screening, although the woman would never have had any trouble from them. The question is, how much over-diagnosis?

The UK study described above says over-diagnosis is far outweighed by lives saved. The researchers claim around 2 lives are saved for every over-diagnosed case. I’ll hold my hand up to admit that, despite poring over the study, I don’t fully understand how they’ve arrived at these figures. The statistical models in the paper are complex and beyond most non-statisticians. (Any statisticians reading, please take a look and let me know what you think!)

For the sake of argument, let’s say both studies are right. Overall, the population of Denmark had no net gain in women’s lives from breast screening. And the UK has had a net gain, one that outweighs the risk of over-diagnosis. I’m using terms like ‘net gain’ for a reason. These studies still don’t answer the initial question – is it worth me, you, your mum, my auntie, going for breast screening?

I don’t know. In Denmark, there are doubtless individual women who owe their lives to having their breast cancer picked up by screening, while it was treatable. And in Britain, there are doubtless women suffering through surgery and chemotherapy, who would never have needed treatment if they’d not gone for mammography. Population-level studies are designed for public health specialists and can only tell us so much. They can’t predict what will happen to you, as an individual.

It comes down, as so often, to what you think about risk. Would you find it impossible to ignore that screening invitation, for fear of missing something that might be fatal in future? Or would you rather wait till trouble found you, blissful in ignorance? What I do think is important is that women are told the truth – or the closest we can get to it – about screening. We can’t promise that all cancers will be picked up by mammography. We don’t know if every cancer picked up this way would have caused trouble. Personally, I’m not convinced we can show for sure that cancer screening saves lives. I’m not alone – see Dr Margaret McCartney’s FT blog on the topic.

I’m still a few years away from that screening invitation dropping through my door. When it comes, I’ll think about my state of health, my personal risk factors for breast cancer, what the researchers say, and make my own decision. I don’t expect it to be easy.

Image: thanks, as always, to Wellcome Images. Credit: Annie Kavanagh.

NOTE: The Guardian’s contract with BMJ for news stories has now ended, so some of the links above no longer work. Apologies.

12 Responses to “Is it worth going for breast cancer screening?”

  1. Adam Says:

    I’m not surprised you’re confused by the statistical models in the Duffy et al paper. I don’t think it’s down to any lack of statistical expertise on your part, it’s just that the model is very poorly explained. I’m a statistician and I didn’t follow their logic either.

    However, I did have a good look at their stats on the assumption that their equations are correct (or at least what I think they meant by their equations, as there was an obvious typo in one of them which didn’t help in understanding what they were doing). What I found was that their results were extremely sensitive to their assumptions, and that makes their conclusions unreliable. In other words, if you had taken a slightly different value for one of the input assumptions, you would have got substantially different results.

    You can read more of my thoughts on the study on my own blog, at

    http://dianthus.co.uk/breast-cancer-screening-part-2

    I’m also concerned that the opacity of the maths leading to their equations may have compromised the peer-review process:

    http://dianthus.co.uk/breast-cancer-screening-and-peer-review

  2. annasayburn Says:

    Thanks very much, Adam. I got my maths teacher husband to take a look, and he said something similar. He also spotted the typo in the equation, which doesn’t fill you with confidence about the peer-reviewing of the rest of the paper.

  3. Deborah Says:

    I couldn’t agree with you more.
    The worrying and insulting thing about cervical and breast cancer screening is that doctors and governments think it’s fine to mislead women, inflate the benefits, exaggerate the risk of the cancer and forget to mention the risk of false positives and over-treatment. They might mention false negatives because that can frighten women into regular “compliance”.

    I’m one of the “defaulters”…I rejected cervical screening 30 years ago after doing my own research. My Dr simply ordered me to have the test; I refused. It shouldn’t be necessary for women to go looking for answers themselves, but all this time later that’s still the case.
    I’m disgusted at the scare campaigns, doctors being “secretly” paid financial incentives to reach screening targets, the lack of risk information and zero respect for informed consent.
    When 99.35% of women (incl the 0.35% who get false negatives) don’t benefit from cervical screening, but 77% of Australian women will be referred at some stage for colposcopy and some sort of biopsy, that’s awful and harmful over-treatment for a very small risk.
    Over-treatment is dismissed as “minor” by doctors, I totally disagree. These procedures are embarrassing, painful and can be damaging – damage to the cervix can lead to infertility, miscarriages, problems during pregnancy (cervical cerclage), more c-sections, premature babies and psych issues.
    Minor?
    At the very least women should be left to judge whether they regard these very likely biopsies and treatment as minor. My sister did not regard her cone biopsy as minor. (it was negative) We now know there are more than 50 cone biopsies that are unnecessary for every one that’s necessary.
    Any other screening test that caused this amount of harm to help a small number would be ruled out as unethical.
    Most women remain ignorant of the high risks of testing and the tiny risk of this cancer.

    Our risk profiles are ignored as well, a very low risk woman is rolled up with high risk….why not give women ALL of the facts and allow them to make their own informed decision?
    Instead we have a hugely expensive screening program that requires 80% of women to screen to have any chance of bringing down an already small death rate (which was falling before screening started anyway and clearly other factors play a part like more women having had hysterectomies these days)
    No one is counting the negatives outcomes and the impact of this screening on the lives of the 99% of women who’d never have an issue with cervical cancer.
    I’ve seen so many women harmed over the years, including my younger sister.
    Papscreen are ramping up the pressure here, only 60% of women screened in 2008-09 and so we’re being chastised like naughty children. We’re apparently “embarrassed” and “busy”, there is never even a vague recognition of the fact some of us have made an informed decision not to screen and we don’t need to make excuses, that’s our right.

    I think more women are working out 2 yearly screening is a bad idea and risks your health, others understand that testing before 25 or 30 is very risky…our program is seriously out of step with the rest of the world. More women are also deciding not to participate at all. (having got to the facts)
    Breast screening – we’re not getting the sort of risk information here that you’re seeing in the UK, but some of it is drifting our way if we go looking for it. Even after the Nordic Cochrane Institute openly criticised BreastScreen’s brochure, nothing was changed, such is the arrogance of these people.
    Thankfully, we have the paper put together by the Institute but once again you won’t find it at the Dr’s office – you have to go searching.
    I’m finding the ever-increasing demands made on us to “just have” screening, to do as we’re told, paternalistic and unethical.
    It has shaken my faith and respect for the medical profession.
    I don’t have breast screening, I have too many concerns about risk.
    It worries me greatly that the majority of women just accept their doctor’s advice to their detriment…how is it acceptable or ethical to tell women a happy screening story, count the scalps and collect your cheque?
    Many women get angry when anyone criticises screening, maybe these women can’t be reached, many believe screening saved their life when it is FAR more likely they had a false positive and unnecessary treatment…but many women would look at the facts and make informed decisions, if they were given the chance.
    Thanks for your article.
    Did you write the piece in the Guardian in 2003, “Why l’ll never have another smear test”?
    I’ve referred many women to that article over the years and to the research of Dr Raffle and Prof Baum.

  4. annasayburn Says:

    Thanks Deborah – yes, I wrote the 2003 Guardian piece, although I didn’t pick the title and it was a little more absolute than I’d have liked. I’m not against screening per se, but I do believe women should be given a full picture of the facts before they make a decision, and that decision should be respected.

  5. Deborah Says:

    How refreshing, we don’t hear that sort of thing in Australia.
    I also saw a great article by Dr Margaret McCartney recently, another UK/Scottish Dr…”Some women don’t want pap smears” stating the obvious, but how rarely is that concession even made?…in many countries pap smears are an unwritten law, not an offer.
    I feel very sorry for poor American and Canadian women who can’t even get the Pill without annual smears (even though the recommendation was changed to 2 yearly recently) routine pelvic exams, sometimes a rectal exam (in stirrups!) and a breast exam. If she refuses, the woman is refused birth control. That is the norm in that country and all women are pressured to start having routine gyn exams (including virgins) from 18, although ACOG have now called for yearly visits for girls as young as 12-13. Horrifying!
    We really need more voices calling for the rights of women and our bodies to be respected.

  6. annasayburn Says:

    This post seems to have created quite a bit of interest. There’s been more recent research on breast cancer screening, which my colleage Philip Wilson wrote about on the Best Health website, http://besthealth.bmj.com/x/news/540567/news-item.html. Do take a look.

  7. Deborah Says:

    Prof Baum gave an interesting lecture at UCL recently, “Breast cancer screening: the inconvenient truths”. It’s on the Medphyzz site & takes about 35 minutes to listen to the entire lecture, but can I tell you, it’s 35 minutes well spent…and could save you or someone you love from a lot of grief.
    Of course, the current Australian breast screening brochure is very general and doesn’t mention false positives or over-diagnosis at all.
    It is scandalous that we have a double standard in cancer screening. I totally agree with Prof Baum – everyone seems to accept the risks of prostate screening and the recommendations have been downgraded – men have been informed promptly of the actual benefit and risks.
    Yet our screening programs carry on feeding us inaccurate and incomplete information (basically propaganda) and using unethical tactics to achieve govt-set targets. There is zero respect for informed consent and for all the women they harm along the way.
    We really are treated like third class citizens….the thinking is ignore all criticism and carry on harming women – most will never know, so that makes it okay…

  8. Deborah Says:

    That lecture is also on Utube.
    The Letters section of the BMJ also contains some scathing criticism of the new UK breast screening brochure. I don’t believe a govt, medical or womens’ group are capable of drafting an unbiased summary – there are too many snouts in the trough or misguided hysteria. The job should be given to the Nordic Cochrane Institute – they’ve produced a great summary of the risks and benefits of mammograms – shame so few women have read it. The truth threatens these expensive programs – so I fear nothing will really change. It needs to happen from the ground up with more women walking away or demanding the truth, a choice and/or options.

  9. dlb2 Says:

    More damning research on breast screening – research that shows the fall in breast cancer deaths is about better treatments and not screening. Prof Baum has called for a halt to screening and is apparently taking legal action against the NHS (along with others).
    Not much is being said in Australia – we have no real advocates for informed consent in this country – there was a small bit in the paper about this research with the final word going to a pro-screening person. I didn’t hear it mentioned in the evening news.
    This is a red hot topic in the UK, but most women here have no idea there is anything controversial about breast screening.
    Breast Screen is pushing to reach a target of 70% of women in the age range, 50-69 – to hell with informed consent.

    http://www.guardian.co.uk/commentisfree/2011/aug/02/breast-cancer-screening?INTCMP=SRCH

    (the link to the article in the BMJ is in comment 3 or 4)

  10. Patty Stewart Says:

    The best screening is thermography.Cancer creates its own blood vessels, which are warm and therefore detected by thermography. Angiogenesis is the term for the creation of the blood vessels. Inflamatory breast cancer has no lumps to speak of and can be detected by thermography. Also women who have dense breasts have lumps missed regularly by mammography, but not by thermography. Plus I don’t want the extra radiation. If something comes up on my thermograph, I will elect for ultrasound.

  11. Anna Sayburn Says:

    Patty, I’ve not heard of thermographic cancer screening. I’d want to see some very good quality evidence before I decided to use any screening test not already part of an established programme.

  12. Eliz52 Says:

    You have to be just as careful of tests that ARE part of an established program. Our cervical screening program is excessive and harmful – and a review is only now starting, so women who trust their doctors will continue to be horribly over-screened for years to come…
    It is very concerning when things can be marketed as health care and in our best interests when in fact, they’re controlled by those who are motivated by things other than our best interests – they basically don’t give a damn about women.
    I look at countries like the Netherlands and Finland and even the UK and they seem to get things done – they move with the evidence and keep their programs current, empowering women with options and information.
    Not here – it’s an exercise in harmful excess and all other options are closed off to us. I see Tampap is available in the UK – not here…
    Thankfully, more women are refusing to be over-screened and are getting the answers they need from overseas sources. I have a colleague who is using a hrHPV primary self-test in Amsterdam at the moment with the assistance of one of their doctors – she wants to find out once and for all whether she’s even at risk from this rare cancer. This option is unavailable here and her doctor even tried to say this testing is unhelpful and she should just have 2 yearly pap tests until she’s 70 (and no doubt with that much testing, a false positive and perhaps, unnecessary biopsy or procedure) Our doctors work for the program and are happy to over-test and harm their patients in return for target payments, some are even happy to lie and mislead their patients to protect the program.
    We have only just been told about the risk of over-diagnosis by one of our brave doctors – nothing has been done, the Minister of Health has made no comment – few doctors (if any) have supported Assoc Prof Bell – so it seems the issue will be left to die and then back to the business of screening women with no informed consent.
    I think it says a lot about our medical profession and it’s not flattering…


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