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Breast screening benefits outweigh harms, finds major study

The benefits of breast cancer screening outweigh the harms of over-diagnosis, a major European review has concluded.

Researchers reviewing established screening programmes across 18 European countries, including the UK, concluded that lives saved by mammographic screening outweigh over-diagnosed cases by two to one.

The review of European studies, published in the Journal of Medical Screening,focused on the impact of screening over the past 20 years on breast cancer mortality, the over-diagnosis of cancer cases and false-positives screening results.

It found that on average, for every 1000 women screened every two years from aged 50 to around 69, an estimated seven to nine lives were saved and four cases were over-diagnosed.

For every 1000 women screened, there were 170 having at least one recall followed by a non-invasive assessment with a negative result, and 30 women having at least one recall followed by invasive procedure, yielding a negative result. 

Members of the EUROSCREEN working group that carried out the study, including Professor Stephen Duffy, professor of cancer screening at Queen Mary University's Wolfson Institute of Preventive Medicine, said the findings should be clearly communicated to patients through a ‘benefit and harm balance sheet' when they are invited for screening.

‘The intention is to ensure that women are fully aware of the chief benefit and harms when they decide whether or not to attend screening', the authors said.  

A US study published earlier in the year found that up to a quarter of women diagnosed with breast tumour under mammography screening would never develop a malignancy.

And the authors concluded that the study showed a ‘substantial ethical and clinical dilemma' over whether screening programmes should exist. 

The authors of the latest study point out that the cumulative risks of breast cancer incidence and mortality in the absence of screening were calculated from the age-specific rates observed in 1985 to 1986 and breast cancer incidence and mortality rates have changed over time.

Consequently, the estimates of lives saved and over-diagnosed cases were approximations.

But they added that the figures ‘clearly indicate, however that the relationship between benefit and harm of mammographic screening is much more favourable than some recent publications suggest'.

‘A comprehensive review of European studies of service screening shows that population-based mammographic screening is contributing to the reduction in breast cancer mortality in the EU, achieving a mortality benefit at least as great as they observed in the RCTs,' they concluded.

‘Furthermore the estimated number of breast cancer deaths avoided by screening clearly exceeds the estimated number of cases of over-diagnosis.

‘These results are intended to help a woman who is invited to screening to make an informed personal choice about the possible outcomes and the implications of participating in screening'.

Dr Margaret McCartney, a GP in Glasgow, told Pulse that a randomised controlled trial was needed to fully establish the benefits of breast screening.

‘It's important to ask what is gained from looking at the data presented compared with for example the Cochrane reviews of randomised controlled trials. Estimating reductions in breast cancer deaths from screening programmes are very hard to do accurately without RCTs - as indeed are the harms of overdiagnosis.

‘Using case controlled studies to estimate benefits are fraught with difficulty and are not recommended by the WHO - if we want to think about evidence based assessments, it's RCTs assessed by independent observers that we should be referring to'.

But in an accompanying editorial, Professor Allan Hackshaw, professor of epidemiology and medical statistics at the Cancer Research UK and UCL cancer trials centre, said the authors set a precedent on how to monitor the latest data.

‘What these papers tell us is that the time has come to move away from relying solely on the older randomised trials of mammographic screening for the evidence base, and to use data regularly collected and monitored from service screening programmes, with proper statistical analyses in addition to the results from randomised trials,' he said.

 

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