Breast screening is beneficial, panel concludes, but women need to know about harmsBMJ 2012; 345 doi: http://dx.doi.org/10.1136/bmj.e7330 (Published 30 October 2012) Cite this as: BMJ 2012;345:e7330
UK women invited to attend screening for breast cancer are three times as likely to be treated for a cancer that would never have harmed them as they are to have their lives saved, an expert panel has concluded.1
For every 10 000 women invited to mammography screening for 20 years between the ages of 50 and 70, the panel estimated that 43 deaths would be prevented and 129 women would be given a diagnosis (and most likely treated) who did not need treatment.
The panel’s calculation of the lives saved is close to that previously claimed by the NHS breast screening programme: 1300 a year. But 4000 women undergo treatment for a cancer that would not have harmed them.
The panel, assembled by the Department of Health for England and the charity Cancer Research UK, concluded that screening confers significant benefits and should continue but that clear communication to women of the harms and benefits was essential.
England’s national director for cancer, Mike Richards, said that he accepted the findings as “the best we’ve got” and that they would be incorporated into leaflets sent to women inviting them to be screened.
Cancer Research UK said that it advised women to continue attending screening. Harpal Kumar, the charity’s chief executive, said, “On balance, taking all the evidence into account, CRUK recommends that women go for breast screening when invited.”
The panel, chaired by Michael Marmot, professor of epidemiology and public health at University College London, was set up to try to resolve arguments over the risks and benefits of mammographic screening, with an expert membership that excluded anybody directly involved in the screening programme. It was launched at a London press conference in the absence of Marmot, who had a serious bicycle crash and broke his leg on his way to the meeting. David Cameron, clinical director of the Edinburgh Cancer Research Centre, said that the panel had reviewed the extensive literature on the subject but had not conducted a formal systematic review.
The panel’s assessment of the risks, Cameron agreed, was a little higher than people had previously thought. Richards said that the findings would be used to inform a new assessment of the cost effectiveness of breast cancer screening, as well as a new information leaflet.
The present leaflet mentions the possibility of harms but does not quantify them. Richards said that he could not prejudge the outcome but expected a new leaflet to be drafted within about four months. The committee responsible held its first meeting on Monday 29 October.
In spite of the huge literature, the panel’s estimate of harms came from just three randomised controlled trials, the only three of 11 randomised controlled trials of breast cancer screening that did not just automatically allocate the control group to screening at the end of the trial period and that followed these women for several more years after screening. These three trials were carried out in Malmö, Sweden, and in Canada. They showed that among the women who were screened for 20 years and then followed until the end of their lives about 19% of the cancers diagnosed during the screening programme would not have led to harm and thus represented “overdiagnosis.”
Cameron explained that these were not “false positives” but actual detections of cancers that would not, if left untreated, have done any harm. For 10 000 UK women screened from age 50 for 20 years, 681 cancers would be found, the panel estimated, of which 129 would fall into the overdiagnosis category. Unfortunately no methods yet exist for identifying which of the cancers detected pose no threat, so all these women would be offered treatment and almost all would receive it. Of the roughly 307 000 women aged 50 to 52 who were invited to screening every year, just over 1% would have an overdiagnosed cancer during the next 20 years. One woman in 250 would have her life saved, in round terms, and one woman in 77 would face treatment she did not need.
Marmot said in a statement, “For each woman, the choice is clear. On the positive side, screening confers a reduction in the risk of mortality of breast cancer because of early detection and treatment. On the negative side is the knowledge that she has perhaps a 1% chance of having a cancer diagnosed and treated that would never have caused problems if she had not been screened. Clear communication of these harms and benefits to women is essential and the core of how a modern health system should function.”
How women will react to this balance of risk and benefit is not clear, but Cancer Research UK said that surveys indicated that women would rather not take the risk of declining mammography.
Anne Mackie, director of the UK National Screening Committee, said, “As with all screening programmes, there is a balance of benefits and harms to weigh up, and it is crucial that the public get fair and balanced information so they can make an informed choice. We keep all screening under regular review, taking on board the latest evidence every time we do so—this independent report makes an important contribution to that.”
Richard Winder, deputy director of NHS cancer screening programmes, said, “This was a robust review, and we appreciate the rigour and efforts of the panel in conducting it. We are pleased that the panel concluded that the NHS breast cancer screening programme confers significant benefit and should continue. Where they have made recommendations, we will work with all partners to take these forward.”
Peter Gøtzsche of the Nordic Cochrane Centre, who has long been a critic of breast screening, said that the panel had narrowed the uncertainty about screening but that the balance between benefit and harm was still three times more positive than his own Cochrane review.2 He said that it was disappointing that the panel had ignored rigorous observational studies that had failed to show any benefit of screening and that its assumption that the benefits of screening and of better treatments were independent was “simply not true.”
He added that the panel’s estimate of overdiagnosis was too low because it was based on relatively short trials. Overdiagnosis increased the longer the time period, because many cancers detected through screening would have disappeared spontaneously without treatment, he said.
“The panel does not take this into account, and its estimate of the balance between benefit and harm is much too positive,” Gøtzsche said. He said that the rate of overdiagnosis was much higher than the panel believed.
Cite this as: BMJ 2012;345:e7330
bmj.com Observations: The NHS breast screening programme needs independent review (BMJ 2011;343:d6894, doi:10.1136/bmj.d6894); Observations: An independent review is under way (BMJ 2011;343:d6843, doi:10.1136/bmj.d6843); Analysis: Screening for breast cancer—balancing the debate (BMJ 2010;340:c3106, doi:10.1136/bmj.c3106)