Mammographic screening: give us the facts
Authors: H. Thornton
Journal: Journal of the Royal Society of Medicine (2003)

Few interventions in medicine, public health or otherwise, are without potential harm. Lately, a group in Bristol looked at the impact of the local cervical screening programme.1 Raffle and her co-workers reckoned that about 1000 women need to be screened for 35 years to prevent one death. The potential harm from this programme arises from overdetection. The Bristol workers calculate that, for younger cohorts, the lifetime incidence for any cervical abnormality could reach 30-40%, with much unwarranted anxiety from medical interventions. And this, they say, is not the only resource-intensive NHS cancer screening programme with scope for major harm from tests and treatments.

At an RSM meeting on breast cancer, David Purdie drew attention to inflated popular notions of breast cancer risk.2,3 Doctors, he declared, should do more to emphasize that absolute risks are low—a point reinforced by Ali Kubba when considering the slightly increased relative risk associated with combined oral contraceptives in young women.4

It is healthy citizens, with less incentive to inform themselves than ‘patients’, who are most in need of such information. The RSM meeting closed with a debate on the motion, ‘This house believes that the benefits of breast screening outweigh its risks and costs’, in which I spoke for the opposition—though I concluded by advising the audience to abstain from voting, as ‘the only wise and proper course’. There is no way at present to ‘weigh’. The harms may be physical, psychological, financial, intergenerational5 or social. The result of this debate, in which abstentions were unfortunately not counted, was reported gleefully on the NHS Cancer Screening website as ‘100 per cent vote in favour of the effectiveness of breast screening’. Aside from the inaccuracy, concentration on the outcome of ‘effectiveness’ to decrease mortality in a population denies and dismisses considerations of human rights. There is a moral imperative to provide unbiased, accurate information, not only about possible benefits, but also about the inherent limitations, consequences and risks.

Underpinning a cancer screening programme is the notion that there is scientific certainty both about ‘knowledge’ itself and about the measurement and computation of harms to populations or individuals. But how can the evidence from research studies be objectively conveyed when even ‘the experts’ are in contentious disarray? Perhaps women currently regard screening as similar to the National Lottery—i.e. you participate more in hope than in expectation. Most women base their decisions on perceptions from media presentations, influenced too by NHS leaflets that ignore General Medical Council guidelines on consent.6 In my judgment, uptake of the mammography programme depends on inflated ideas of individual risk coupled with a misconception about the power of screening. What underlies the tendency towards inadequate communication with these ‘worried well’ people and ‘pseudo-patients’?7 One might think that the ethical imperative and obligation to inform about risks would be exceptionally strong in these circumstances, where the invitation to attend comes from the doctor (a reversal of the usual relationship). The theory of responsibility describes three levels of decision-making. In the first, we make a decision for ourselves; in the second, a physician makes a decision for a patient; and the third is a recommendation for a population. The last, of which screening is an example, is the most rigorous and demands a strong evidence base. The point was made by Cochrane and Holland three decades ago:


‘If a patient asks a medical practitioner for help, the doctor does the best possible. The doctor is not responsible for defects in medical knowledge. If, however, the practitioner initiates screening procedures the doctor is in a very different situation. The doctor should, in our view, have conclusive evidence that screening can alter the natural history of disease in a significant proportion of those screened.’8


In 2001 a systematic review questioning the value of mammography was reported by Olsen and Goetzsche.9 The passion of the reactions to this publication is instructive. Emotions do run high when health professionals in the screening industry and ‘believing’ women join to defend a much publicized and cherished programme. None of us doubts the benefits it brought in both raising awareness and in improving quality of diagnostic procedures. But this very success has shifted the spectrum of detection so that ‘too early’ (rather than ‘early’) neoplasms are being found, resulting in dilemmas for doctors and patients alike. Many women with non-invasive and indolent cancers might have gone to their graves in blissful ignorance had it not been for the zealous pursuit of early cancers in a programme that failed to respect the need for honesty and neutrality when presenting ‘the facts’.10