Posted by: Margaret McCartney31 October 2012
The Marmot review is in. Breast screening has now been officially recognised in the UK to be a mixed bag, with the potential for benefit but also the risk of harm through overdiagnosis and overtreatment.
This is nothing new; it's been available via Cochrane for years.1 But this recognition for British women marks a significant change in how we view screening. It tells us what we already know - except now it is on the front page of the tabloids. Screening can cause harm.
From antibiotics to statins and the last stages of life, GPs deal in uncertainty. We are versed in the weighing of unknowns against each other. Sharing decisions where there is often no correct answer is an aim of contemporary general practice; indeed, the GMC says doctors should ‘provide effective treatments based on the best available evidence’ and ‘give patients information they want or need in a way they can understand; respect patients' right to reach decisions with you about their treatment
Yet the immediate response of Breakthrough Breast Cancer, the Breast Cancer Campaign, and Breast Cancer Care was to join together and say that the review had brought ‘much needed clarity- screening can save lives’.3
They added: ‘This is good news for women as they can now be assured that breast screening can be beneficial... some women who attend screening may be diagnosed and treated for a cancer that may not have caused them harm in their lifetime... We encourage all women to attend their screening appointments.’4
I find this amazing, in a sad way. The cancer charities are thus making a value judgement that women should take part in a program which, the review found, gives a 43 in 10,000 chance over 20 years of delaying your death due to breast cancer - and which will overdiagnose 129 women over the same period, thus exposing them to treatment they cannot benefit from.5 The chance of being harmed
by unnecessary treatment is far more than the chance of extending life due to the screening; for every death delayed from breast cancer, three women are treated unnecessarily.
So what should women do? If we really mean what we say by informed choice, we must allow women the autonomy to decide for themselves. This includes the right for women to make choices that their doctor - or the director of a charity- might personally disagree with.
So are these large cancer charities are best placed to inform women of their options? Only one UK charity that I know of, the small Challenge Breast Cancer in Scotland, has long called for fair information on screening to be given to women.
For despite the enormous amount of 'awareness' about breast cancer, most women do not know that age is a large risk factor for breast cancer and most overestimate the benefit of mammography.6,7 We have to stop focussing on the throwaway advertising lines which 'awareness' campaigns ride on, and concentrate on evidence-based knowledge.
Some women will have rotten bad luck and have breast cancer with no apparent risk factors. But how many other women know about the effects of being overweight or excess alcohol on cancer risk; and how much investment is going into reducing population risks through evidence-based legislation on food or alcohol? I'm concerned that we have been 'pinkwashed' by screening, which has been oversold to the extent that we are overlooking other interventions which could be less harmful and more beneficial.
It is now up to the UK National Screening Committee to evaluate the cost effectiveness of breast screening. They will no doubt bear in mind that the review was clear that their numbers were best estimates, not proven facts; that they focussed on breast cancer rather than all cause mortality, which can overestimate screening benefit; and they will also know that the trials they focused on are up to two decades old, which means that the effect of newer, better breast cancer treatments isn't going to be visible, and may produce different screening effects.
The Informed Choice about Cancer Screening consultation is due to report in November and is likely to herald a sea change in how we describe risk and benefit to patients, via new, evidence-based information leaflets. And I predict then GPs will be busy doing what they do best: helping people deal with uncertainty as best, and as independently, as we can.
1 The Cochrane Library. Screening for breast cancer with mammography. 2008. http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD001877.pub4/abstract
2 The GMC. Good Medical Practice: Providing good clinical care. http://www.gmc-uk.org/guidance/good_medical_practice/good_clinical_care_inde
3 The GMC. Good Medical Practice: Duties of a doctor. http://www.gmc-uk.org/guidance/good_medical_practice/duties_of_a_doctor.asp
4 The Breast Cancer Campaign. http://www.breastcancercampaign.org/
5 Independent UK Panel on Breast Cancer Screening. The benefits and harms of breast cancer screening: an independent review. The Lancet 2012. http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(12)61611-0/abstract
6 Moser K. Do women know that the risk of breast cancer increases with age? BRCGP 2007. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2047017/?tool=pubmed
7 Dominighetti G et al. Women’s perception of the benefits of mammography screening: population-based survey in four countries. Int J Epidemiol 2003. http://ije.oxfordjournals.org/content/32/5/816.long