Mass breast-cancer screening using mammography – a type of x-ray that looks for abnormalities – is passionately advocated by many in the belief that women’s lives will be saved. Many wealthy countries have adopted it as the key plank in efforts to reduce the toll of the disease. Therefore, when the Canadian National Breast Screening Study found no benefit from this type of programme there was a lot of concern.
The latest analysis of this study, which I directed, compared the incidence of breast cancer and deaths from the disease over a 25 year period in thousands of women aged 40 to 59. When the study began, whether women did or didn’t undergo mammography screening was decided at random. We found there was no difference in mortality between the two groups, but overdiagnosis in the mammography group was significant.
As a result of this and other studies, the Swiss medical board took the pioneering step of recommending that mass mammography screening there should be abolished.
Of course my colleagues and I weren’t the first to conclude that the benefit of mammography is vanishingly small, and that the detriments far outweigh the advantages. We confirmed that those detriments include labelling lesions detected by mammography as cancer even when they do not progress like cancer and are therefore not destined to kill. This is overdiagnosis, and it can lead to unnecessary treatment and harm to health.
The upshot is that the head start gained by earlier diagnosis using mammography – assumed to be four years on average – is in fact just one year. Given that breast cancer has a long natural course – nine years or more – this is a relatively unimportant gain and explains the lack of benefit seen in our study.
The women who took part and weren’t receiving routine mammography did take other steps to detect breast cancer early. All were taught breast self-examination during their first check-up, and those aged 50 or over returned for four annual breast examinations during the period of the screening trial.
Many cancers were found as a result. We discovered that women who developed breast cancer fared better in survival terms if they practised self-examination well than if they did it poorly.
What are women to do now? First, they should emulate the participants in our study who didn’t have mammography – that is, practise breast awareness, have annual breast examinations and ensure that if they detect an abnormality they are checked by a doctor.
Second, women should take steps to reduce their risk of developing breast cancer; steps that also reduce the risk of other diseases. These are to stay physically active, avoid weight gain – especially after the menopause – eat a diet low in fat and red meat and high in fruit and vegetables, and start these steps as early in life as possible.
The responsibility for reducing the risk of breast cancer doesn’t rest only on women, but also on those in charge of healthcare the world over.
In countries with modern healthcare systems, such as the UK, US, Canada and Australia, our results suggest the rationale for screening by mammography should be urgently reassessed. Education, early diagnosis and excellent clinical care should of course continue to be provided to ensure that as many breast cancers as possible are diagnosed at a small and treatable stage.
Mass use of mammography turns out to be a comfort blanket that offers no real gain. It is time to let it go.
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