Routine breast cancer screening does reduce death risk, an independent panel of experts reported in The Lancet. However, the practice also results in overdiagnosis; cases of women with false positive results, having to have unnecessary biopsies and other interventions, or patients undergoing treatment for harmless tumors.
Experts and patient groups have been debating when breast cancer screening should start, and how often it should occur. It used to be once a year as soon as the woman is 40. However, because of the number of false positives, needless biopsies, extra financial costs, and the distress overtreatment causes, the experts now say “it depends”. The American Medical Association, in July 2012, said women should be eligible for screening mammography from the age of 40, and it should be covered by insurance.
Breast screening tends to detect breast cancer earlier on during the disease, resulting in prompter treatment and a better prognosis.
However, there has been concern about the number of cases of overdiagnosis. Overdiagnosis, for example, is when a tumor is detected during screening, the woman has the lump surgically removed, receives radiotherapy and medication. However, the tumor, if it had not been detected, would have done the patient no harm; she would have spent the rest of her life with an undetected tumor that never caused illness. The problem with mammography is that it does not distinguish between progressive and non-progressive cancers.
The Independent Panel of experts on Breast Cancer Screening consisted of:
- UK M G Marmot (Chair, UCL Department of Epidemiology and Public Health, UCL, London)
- D G Altman (Centre for Statistics in Medicine, University of Oxford)
- D A Cameron (Edinburgh Cancer Research Centre, University of Edinburgh)
- J A Dewar (Department of Surgery and Oncology, Ninewells Medical School, Dundee)
- S G Thompson (Department of Public Health and Primary Care, University of Cambridge)
- Maggie Wilcox (lay member)
The Panel was set up by Professor Sir Mike Richards, The National Cancer Director for England, and Dr Harpal Kumar, Chief Executive Officer of Cancer Research UK. The aim was to provide “an independent review of the evidence for the benefits and harms of breast cancer screening in the UK”.
The Panel’s aim was to analyze existing evidence for breast cancer screening effectiveness versus over-diagnosis risk. They gathered data on 11 randomized, controlled trials which focused on whether breast cancer screening led to fewer breast cancer deaths, compared to when no screening is done.
They found, overall, that patients who are invited to have a mammogram have a relative risk of breast cancer death that is 20% lower than those who are not invited.
The Panel said the studies had some limitations, e.g. they were all over two decades old. However, they still concluded that, according to the evidence they examined, the relative risk of dying from breast cancer is 20% lower for women who go to routine screenings.
There were only three randomized trials on overdiagnosis as a consequence of routine breast cancer screening. Despite this, the Panel concluded that of the approximately 307,000 females aged 50 to 52 who had been invited to start screening annually, slightly more than 1% were over-diagnosed over a 20 year period.
They concluded, after collecting data on the benefits and overdiagnosis, that for every 10,000 British women who are invited to screening from 50 to 20 years of age, approximately 681 will have a cancer detected, of which 129 will be cases of overdiagnosis; and 43 breast cancer deaths will be prevented.
They added that further research is required to assess the benefits and harms of breast cancer screening.
Professor Marmot said:
“The reduction in risk of death from breast cancer screening corresponds to one breast cancer death prevented for every 235 women invited to screening, and one death averted for every 180 women who attend screening. The breast screening programmes in the UK, which invite women aged 50 – 70 years to screening every 3 years, probably prevent around 1300 breast cancer deaths every year. However, our estimates also suggest that each year around 4000 women are overdiagnosed as a result of screening.
For each woman, the choice is clear. On the positive side, screening confers a reduction in the risk of mortality of breast cancer because of early detection and treatment. On the negative side, is the knowledge that she has perhaps a 1% chance of having a cancer diagnosed and treated that would never have caused problems if she had not been screened. Clear communication of these harms and benefits to women is essential, and the core of how a modern health system should function.”
An Editorial, which was published adjacent the Review, concluded that the UK breast-screening program prolongs lives. Overall, the benefits do appear to outweigh the harms.
The authors wrote:
“Dissemination of these findings is now imperative in the media, the NHS screening programme, and between doctors and their patients. Women need to have full and complete access to this latest evidence in order to make an informed choice about breast cancer screening.”
A comprehensive review of millions of mammographies in Europe, which was published in the The Journal of Medical Screening (September 2012 issue), concluded that the benefits outweigh the harms of over-diagnosis, in terms of lives saved. The authors, from Queen Mary, University of London, showed that for every 1,000 women aged from 50 to 69 who undergo a mammogram every two years, screening saves from seven to nine lives, plus four cases of over-diagnosis.
A Swedish study published in the Journal of the National Cancer Institute (July 17th, 2012 issue) showed that breast cancer screening has limited or no impact on breast cancer mortality among females aged from 40 to 69 years.
Written by Christian Nordqvist