You may have read stories about people who believe their lives were saved because of a routine screening for a disease such as cancer. Or you may have heard of people who feel they were let down because they didn’t receive such screening. While they make compelling media stories, this kind of media coverage of screening is often incomplete and misleading.
It has helped to create unrealistic expectations of what screening programmes are and what they can deliver. On the one hand, there is a mistaken belief that screening only offers benefits. On the other, there is the myth that screening is only offered to certain age groups due to financial restrictions.
This superficial view has real and lasting implications for citizens, patients and health care professionals, leaving many people confused about screening. It needs to change.
Screening involves testing apparently healthy people to see if they have a higher risk of a disease. This means you can offer treatment or advice at an earlier stage, giving a greater chance of successfully dealing with or preventing the condition. Screening programmes are based on careful calculation, including who will benefit, what treatments are available and the level of accuracy of the tests.
Each screening programme is targeted to a specific subset of the population. For example, screening for diabetic eye disease only involves people with diabetes. Other effective screening programmes in the UK include looking for cystic fibrosis in newborn babies, or Hepatitis B and HIV in pregnant women.
But despite what you might read or hear, there are real risks of screening programmes, even in well-established programmes such as mammography. Sometimes screening produces false negative results, where people are mistakenly told they don’t have the disease. More common are the false positives, where people are mistakenly told they have the risk marker when they don’t, or when the condition that is identified would not have progressed, or was harmless. This means that any treatments they were then offered and underwent were unnecessary, with all of the emotional and health consequences that this brings.
Risk versus benefit
There is heated debate about the harm this causes. For example, in the case of UK women aged 50 screened for breast cancer for the next 20 years, one death is prevented for about every three over-diagnosed cases identified and treated. And there is no impact on death overall from all causes.
I am saddened when I hear people discuss their distress about their own or their family member’s “cancer” diagnosis via screening when, for example, the breast cancer cells discovered haven’t developed the ability to spread. These “DCIS” cells look like cancer down a microscope but they don’t behave like cancer and might never have led to a problem.
Women are then put into a terrible dilemma. Do they live with uncertainty, or do they live with life-changing treatments? Would they have ever have started this journey had they realised the uncertainty? How do they get off the conveyor belt now they are on it? In many cases, they do not even realise that the life-changing mastectomy (or double mastectomy) was an adverse consequence of being screened. It seems counter-intuitive, but there is evidence a mastectomy is less likely if you wait for symptoms instead of being screened.
The question of who should be invited for screening generates some of the most emotive and often misinformed discussion. Campaigners and celebrities call for screening in more people, more diseases and for longer with no mention of the impact and potential harms of doing so. It is vanishingly rare that they have any expertise in biology, medicine, science or uncertainty and yet their opinions that “more should be done” or “more could have been done” are given a great deal of airtime.
The conversations surrounding cervical screening are no exception. Currently cervical screening in the UK is only offered from the age of 25, but media coverage and petitions have demanded the cervical screening age be lowered to 20. But research has shown that screening this younger age group is ineffective. It does not prevent deaths from cervical cancer and results in many false positives and overdiagnosis.
No short cut
Treatment of more and more women with minor cellular abnormalities in the cervix will lead to surgical damage and to some cases of premature and damaged babies being born. The cervical screening programme on offer, as with all others, should be based solely on the balance of benefit and harm. It should not be unduly influenced by public discussion that only promotes a one-sided story of benefits.
Screening is not a short cut to health. It should not be for everyone. It should not be for all diseases. It should not be about screening more people for longer. It should only be offered when there are more benefits than risks.
The charity Sense About Science has launched a new edition of Making Sense of Screening to tackle the widespread myths about screening programmes. I hope it will be shared among clinicians, health professionals and anyone interested or concerned about screening so that more people understand that simplistic calls for more screening are wrong. Harms always need to be weighed against benefits when making decisions about screening, whether at national programme or individual level.
Susan Bewley has been Honorary Professor of Complex Obstetrics, at Kings College London since 2011-date, having been a consultant obstetrician and clinical director at Guys & St Thomas' Hospital and NHS London for many years. Her wide-ranging research interests focus on severe maternal morbidity and violence in pregnancy.