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The national breast cancer screening programme, introduced in 1988, gave promise in reducing mortality of the most common cancer in the UK (1). Inviting women aged 50-70 to breast screening every three years allows tumours to be detected at the earliest stage possible. This facilitates less aggressive treatment, improves prognosis, and ultimately aims to increase likelihood of patient survival. The breast cancer screening programme has proven success, with over 13,000 invasive breast cancers detected in one year, and an estimated 20% reduction in mortality in women invited to screening (2).
However the programme has not been without its critics, and there has been a continual debate on whether breast screening does more harm than good. The issues of the screening programme span from inadequate cost effectiveness to overdiagnosis, and also drawbacks in trial design.
Cost Effectiveness
Firstly, the breast cancer screening programme is known to be expensive, and there have been numerous calls for the cost effectiveness to be reassessed. The National Institute of Health and Care Excellence (NICE) uses a threshold of £20,000-30,000 per quality adjusted life year (QALY) to determine whether a health intervention should be funded through the NHS. This means exceptional circumstances would be needed to spend more than £30,000 on one QALY – which is equal to one year of life in perfect health. A 2013 study used Probabilistic Sensitivity Analysis (PSA) to assess cost effectiveness of breast screening. This model is used in health economics to allow uncertainties in parameters to be taken into account by assigning them a distribution rather than a single value. In this case, examples of parameters include the cost of screening the female cohort, and the cost of treating a patient detected early by screening compared to a clinically detected patient. Using a range of plausible scenarios, the programme was found to be cost effective (at the £20,000 per QALY threshold) only 45% of the time. There were huge changes in estimates, which ranged from a reduction in QALYs to the screening programme representing excellent value for money. Almost one-fifth of the model results even estimated cost per QALY to exceed £100,000. This highlights the complexity of calculating cost effectiveness for a screening programme – an intervention which has small effects over long time scales (3).
Overdiagnosis and Overtreatment
The costs of the breast cancer screening programme are not just financial ones. Like any medical procedure, mammography is not accurate 100% of the time – resulting in false positives and false negatives. High sensitivity of testing leads to one of the key drawbacks within the screening programme – it reduces breast cancer mortality but at a cost of overdiagnosis and overtreatment (3). Overdiagnosis results from breast screening being unable to predict prognosis of detected tumours, meaning women undergo treatment for cancers which would not have become harmful or clinically apparent throughout their lifetime (4). Associated overtreatment has both physical and psychological implications for the patient, such as treatment side effects and increased rate of anxiety and depression in those diagnosed. For every 10,000 women aged 50 invited to the UK breast cancer screening programme, there is an estimated 129 cases of overdiagnosis. However within this same cohort, 43 deaths would be prevented by screening, giving the figure of 3 cases of overdiagnosis per death prevented – adding further debate as to whether the benefits outweigh the harms (2).
Uncertainties in Trial Design
Further uncertainties in the benefits of breast screening result from the insufficient sample sizes or inappropriate patient cohorts used within trials which have contributed to the decision-making processes. The 1986 Forrest Reportled to the introduction of a national breast screening programme (5). The recommendations were based on data from trials undertaken in the United States and Sweden, which found the beneficial effects of screening to be concentrated in women aged 50 and over. However, the relevance of these older trials to present-day screening is continuously questioned. Also, when assessing the effectiveness of a screening programme, the scale of trials required in order to get meaningful results is a key problem. Although reductions in mortality have been observed in randomised controlled trials, the figures were not always statistically significant. Furthermore, use of ‘average lifespan with cancer’ as supporting evidence for the screening programme has received criticisms. Since survival is measured from time of diagnosis, early detections through screening automatically increase patient lifespan, even if earlier treatment has no effect on age of death. This is known as ‘lead-time bias’, and should be considered when comparing screened and unscreened populations.
An in-depth look at the breast cancer screening programme reveals both its benefits and drawbacks. Clear communication of these is essential for the success and public understanding of the methods to reduce breast cancer mortality. Justifying the costs of the programme is especially relevant at the moment, upon expansion of screening to women aged 47-73. The Polygeia Breast Cancer Screening Research Group will concentrate on what clinical and economic factors contributed to the programme’s acceptance, as well as providing policy recommendations for the future.
Sophie Caseby is an MSc Integrated Immunology student at Oxford. Her initial interest in global health was in the control of infectious diseases, and she is currently working on vaccines for emerging pathogens at the Jenner Institute. Sophie is now looking forward to expanding her knowledge into health economics whilst co-editing Polygeia’s Breast Cancer Screening project.
References
Cancer Research UK. Breast screening statistics. 2012. Available from: http://www.cancerresearchuk.org/health-professional/cancer-statistics/statistics-by-cancer-type/breast-cancer/screening
Independent UK Panel on Breast Cancer Screening. The benefits and harms of breast cancer screening: an independent review. The Lancet. 2012 380(9855):1778–86.
Pharoah PDP, Sewell B, Fitzsimmons D, Bennett HS, Pashayan N. Cost effectiveness of the NHS breast screening programme: life table model. BMJ. 2013; 346(may09_1):f2618. Available from: http://www.bmj.com/content/346/bmj.f2618
NICE. Scenario: Breast screening. NICE Clinical Knowledge Summaries. 2011. Available from: http://cks.nice.org.uk/breast-screening#!scenario
Forrest P. Breast cancer screening. Report to the Health Ministers of England Wales Scotland and N Ireland by a working group chaired by Professor Sir Patrick Forrest. HMSO. 1986. Available from: http://www.cancerscreening.nhs.uk/breastscreen/publications/forrest-report.html