Does breast screening do more harm than good?
A new UK review of the benefits and harms of screening is welcome, but what we really need is better evidence.
In November 2010, a group of 27 experts from around the world – including myself – wrote a letter that was published synchronously in the British Medical Journal (BMJ) and The Times (London). We reviewed the emerging evidence that challenged the status quo about screening mammography, describing new evidence that suggested the estimates of benefit had been exaggerated and the estimates of harm had been understated.
We described the benefits in absolute numbers rather than as relative-risk reductions. The rather impressive relative-risk reduction in breast-cancer mortality – now accepted as 15 per cent – translates in absolute terms into the need for 2,000 women to be screened over 10 years in order to avoid one death from breast cancer. Incidentally, there is no evidence so far that this then translates into a reduction of death rates from all causes. It is therefore somewhat misleading when the screening industry claims that it is saving lives.
Our leading concern about the harmful side was the unequivocal evidence concerning the overdiagnosis and overtreatment of breast cancer detected at screening. Screening detects many abnormalities that, if left undetected, would never have emerged to threaten a woman’s life. Overtreatment of these indolent ‘pseudo-cancers’ has involved surgery, radiotherapy and chemotherapy. Furthermore, contrary to all the promises of the screeners, mastectomy rates have increased in absolute terms in the population screened. There is another negative consequence of screening: radiotherapy for early breast cancer leads to an increase in deaths from ischaemic heart disease. Although in absolute terms this increase is modest, it could easily nullify the one-in-2,000 chance of avoiding death from breast cancer provided by breast-cancer screening.
We concluded our letter by suggesting that the time was ripe for an independent review. I was therefore delighted to note that the BMJ has just published a letter from the UK government’s ‘cancer tsar’, Professor Mike Richards, announcing that an independent review will now take place. Yet I also remain deeply concerned about a number of issues raised in his response.
My first concern is that the co-chairmen of the review are to be Professor Richards himself and Harpal Kumar, chief executive of Cancer Research UK (CRUK). Professor Richards is hardly independent, as shown by his comments on radio, television and print newspapers last Wednesday, the day of the BMJ press release. The independence of CRUK can be judged by its website, which calls on the government to do everything it can to improve the numbers of women attending for screening.
The next rather amusing ruling was that this independent review panel would be selected from those who have never previously expressed an opinion, or published a paper, related to screening for breast cancer. It is rather like me being invited to adjudicate on climate change. Nevertheless, I understand and, to an extent, sympathise with Professor Richards’ motives for this. There is no doubt that the experts in this field are completely polarised and any attempt to achieve a consensus amongst the cognoscenti is guaranteed to fail.
I am reminded of the fierce controversy concerning surgery for early breast cancer that raged in the early 1970s. A consensus panel on that occasion, of which I was a member, broke up in disarray. And I think that was the occasion when the expression ‘consensus: nonsensus’ was coined. In the end, it was left to clinical trials comparing radical versus conservative surgery to resolve the debate.
So how should one respond to this polarisation of opinion concerning screening amongst those who have actually studied the subject and published in journals? One could argue that the expert medical-scientific community as a whole has reached the point of group equipoise. When such times occur, it is futile to attempt to arrive at a consensus. The correct approach is to recognise that there is communal uncertainty and then to carry out randomised controlled trials that would truly weigh up the outcomes of both points of view in terms of lives and breasts saved.
Professor Richards, in his letter to the BMJ, describes a clinical trial that is about to start and for a moment my heart lifted at this prospect. With some difficulty I was able to track down the details of this study. But I was dismayed to learn that this huge and expensive trial will simply be comparing the current screening programme, for women between the ages of 40 and 70, with an extended programme that embraces a younger and older cohort. The trial simply does not address the dilemma we face concerning the harm versus benefit of screening at any age. I would therefore urge Professor Richards to postpone the start of such a trial, at least until we have the results of the expert independent review.
However, I have a much better idea for resolving the conflict. Why not use the existing infrastructure of the NHS breast-screening programme for a risk-adjusted approach to screening? We have excellent computer systems that allow us accurately to predict the risk of an individual developing breast cancer. I would suggest that, using these tools, we could undertake a triage.
Those at the very highest risk are the very ones who would benefit from genetic counselling and genetic testing, with screening reserved for those women who test positive but are reluctant to accept prophylactic mastectomy.
At the other extreme are those women with a low to intermediate risk of developing breast cancer and who are 25 to 50 times more likely to die of something else. The most likely cause of death among this population would be cardiovascular disease. These women need counselling on how to avoid cardiovascular disease. As it happens, the lifestyle interventions to reduce the risk of cardiovascular disease – like exercise, avoiding obesity, controlling alcohol intake and eating lots of fresh fruit and vegetables – will also reduce the risk of breast cancer.
Mammographic screening could achieve a much better profile of benefit versus harm than is currently the case among women with a middling risk of breast cancer. I would therefore like to suggest that instead of the randomised controlled trial proposed by Professor Richards we should compare the conventional ‘one size fits all’ approach with the kind of risk assessment/risk management scheme that I’ve just described.
Furthermore, we could use this platform for a secondary randomisation for those women with screen-detected duct carcinoma in situ that would involve active treatment versus active monitoring. This way we will learn something about the nature of these precursor lesions and learn how to predict those that are more likely to progress and those that are more likely to regress. Although this sounds somewhat radical, this is precisely what we are doing in the Protect trial for screen-detected prostate cancer. In the prostate-screening trial, we are randomising early prostate cancer cases into three groups – surgery, radiotherapy and active monitoring – to see which produces the best outcomes and in what circumstances. (As independent chairman of the international steering committee for this trial, I can assure the professional and lay public that the study has been judged ethical and the majority of men recruited accept randomisation and seem to understand that this is the best way of resolving uncertainty.)
I therefore throw myself at the mercy of Professor Richards and beg him to consider this approach as a way of breaking the deadlock, accepting the nature of uncertainty, recognising that the laudable way of dealing with uncertainty is to conduct a clinical trial addressing the main reasons for the polarisation of expert opinion, and not to waste valuable resources on a trial which will provide no useful answer to the current dilemma. It is highly unlikely that one group of experts is 100 per cent correct and another group of experts is 100 per cent wrong; there must be a middle way.
Michael Baum worked for 30 years as a surgeon specialising in breast cancer, and is now professor emeritus of surgery at University College London. He is the author of Breast Beating: A Personal Odyssey in the Quest for an Understanding of Breast Cancer, the Meaning of Life and Other Easy Questions, published by Anshan. (Buy this book from Amazon(UK).)
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