Thousands of women every year have treatment they do not need for breast cancer because of screening – but hundreds of others have their lives saved, according to a major analysis published today.
The UK screening programme prevents some 1,300 deaths a year from breast cancer, according to the analysis.
But about 4,000 women aged between 50 and 70 undergo treatment for breast cancer because of over-diagnosis, the researchers say, usually for disease that would never have troubled them.
The findings come from a panel chaired by Professor Sir Michael Marmot, of University College, London.
The panel, reporting in The Lancet, says it is setting out the "pros and cons" of screening. Its work was commissioned by the Department of Health and Cancer Research UK.
Campaigners said the findings showed that screening does save lives. The programme has been criticised recently for allegedly not giving women the full facts about the risks involved.
The analysis shows that for every 10,000 women who undergo screening, 56 are saved from death through breast cancer and another 168 are over-diagnosed. The panel conducted an analysis of some 11 randomised controlled trials of breast screening to reach their conclusion.
Professor Marmot said: "The Panel concluded that the screening programmes have contributed to reducing deaths from breast cancer in women. But they have also resulted in some overdiagnosis among women who go for screening.
"It is now vital to give women information that is clear and accessible before they go for a mammogram so they can understand both the potential harms and benefits of the process."
Cancer Research UK chief executive Dr Harpal Kumar said: "The independent review shows screening saves lives.
"Screening remains one of the best ways to spot the very early signs of breast cancer, at a stage when treatment is most likely to be successful."
He added: "Because we can’t yet tell which cancers are harmful and which are not, we cannot predict what will happen in an individual woman’s case.
"We think it’s vitally important for women to have access to clear information about breast screening, the balance of benefits and harms and the fact that they could be diagnosed with and treated for a cancer that might not cause them harm."
An editorial in the journal adds: "The Panel’s report, the latest and best available systematic review, shows that the UK breast-screening programme extends lives and that, overall, the benefits outweigh the harms."
The Lancet October 30 2012
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