Routine mammography - is it a worthwhile practice or a dogma being supported by vested interest?

Screening makes sense - you find the disease early and treatment can be more effective - or so one would imagine. Cervical smears, for example, minimally invasive, cheap, sensitive and the implications of false positives are fairly low risk.

However, in recent years the evidence is starting to stack up against the benefits of routine population-wide mammography. Do the vested interests of the providers of the screening service taint the interpretation of the latest evidence? Are we at risk of ignoring good sound science in favour of 'lobbying', or are the pro-screening advocates right?

How do we decide what is reliable evidence?

9 Replies

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  • The popularity of all forms of health screening is based on a misunderstanding of the statistics. No screening test is 100% sensitive or specific. This means that, where a condition only affects a small proportion of the population (which is why we screen for it), there will be far more false positive results than real positive ones, and unnecessary treatment carries its own risks. Not many health professionals, even doctors, understand this. Almost no patients do. The problem is that patients are also voters, so politicians are solidly behind screening, and we have a classic case of argumentum ad populum. Understanding of science by politicians is the lowest it has been for decades, so it can hardly be surprising that they are abusing science.

    The current mammography programme studiously ignores all-cause mortality. The roll-out of the age range extension (to include ages 47-50 and 70-73) is being conducted as a cluster randomised controlled trial. The sponsor has stated that the study is not powered to detect an effect on all-cause mortality, despite a planned sample size of 3 million women. This indicates that there is nothing to detect, so there is no overall benefit of screening on deaths. Obviously this programme costs a lot of money, but again the sponsor has declined to carry out an economic analysis. These are just two examples of where those who are committed to mammography screening refuse to face up to factors which undermine the concept. Ethical review has been less than fully effective, the ethics committees having failed to consider all-cause mortality.

    Yet the effort continues unabated, even to the extent of running TV ads inviting women over 70 years to present for screening. Public Health England agrees that there is no robust evidence to support this, and has failed to respond to requests for evidence, so is in breach of advertising standards. The politicians seem to think they are exempt from the standards that apply to the rest of us.

  • @Majikthyse can you explain - for clarity - why all-cause mortality would be a better measure than, say, just deaths from breast cancer?

  • Because of the risks associated with unnecessary treatment. It is dangerous to assume that whatever intervention you are using is without risks. This is exactly why all trials of new drugs must capture all adverse events, irrespective of presumed causality. Only after the adverse event has been recorded is its association with drug treatment assessed. Nobody can accurately predict what the risks of treatment might be, and nobody should assume that there are none. I do not see why we have one standard for commercially sponsored trials and another less rigorous one for public sector trials.

    It might be argued that even if mammography screening has no overall effect on death rate, it may have a useful effect on morbidity and hence quality of life. But the latter is not being assessed in the age extension trial.

  • It depends what you care more about. If at all costs you wish to void dying of breast cancer rather than something else then mammography might marginally benefit you. But if what you are most concerned about is how long you will live, mammography is of no benefit to you.

  • For anyone who wants a guide to help you get to grips with this debate, see Making Sense of Screening: senseaboutscience.org/resou...

  • Can you confirm that no-one involved in delivering screening services or producing screening equipment has been involved in the development of this article?

    If you could refer to my original question, the issue of bias and vested interest was a central question to be addressed.

  • The guide was written because public expectations about screening don't match what screening programmes can deliver (it is not a guide to promote screening but rather to share its limitations and the calculation of benefits and harms). As with all our guides it gives people a ticket to the debate that's happening in the scientific community. We involved a range of experts, explaining their interests in the guide- and partnered with the Association for Clinical Biochemistry, the Institute of Biomedical Science and the Royal College of Pathologists.

    I have to say that while Who funded the study? and, Are there vested interests? are questions we encourage people to ask- they don’t tell us at all reliably what is dependable. The best research in the world could be that conducted by the least popular or most vested organisation, and vice versa. There are many more questions to ask to assess the validity and status of evidence. For some much more developed thoughts on this, see our Director Tracey Brown's recent article: britishscienceassociation.o...

  • I'm afraid that you didn't answer directly the question about the people who have written your review. Having worked in the healthcare industry for 20 year I am very sceptical about evidence and clinical guidelines being objective when there are vested interests involved. Companies, research charities and the NHS set up their research programmes and choose their methods in a way that support their interests. Clinical guidelines are strongly influenced by industry, through clinicians who have a very carefully nurtured point of view on a procedure or a product.

  • The guide itself has the information you are looking for.

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