Breast cancer screening programs are resulting in the treatment of harmless tumours, an international study has found.
A review by a British panel of experts on breast cancer screening procedures found that for every life saved by screening, three women are overdiagnosed.
Overdiagnosis occurs when screening identifies a tumour, which is consequently treated by surgery, and often radiotherapy and medication, but which would have remained undetected for the rest of the woman’s life without causing illness if it had not been detected by screening.
The scientists found screening in women aged 50 to 70 every three years in the UK probably prevents about 1300 breast cancer deaths each year, but results in about 4000 cases of overdiagnosis.
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Sir Michael Marmot from University College London headed the panel and said women needed to be told about the harms and benefits of screening.
"On the positive side, screening confers a reduction in the risk of mortality of breast cancer because of early detection and treatment," Professor Marmot said.
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"On the negative side is the knowledge that she has perhaps a one percent chance of having a cancer diagnosed and treated that would never have caused problems if she had not been screened."
The director of Australia's Macquarie University Cancer Institute, John Boyages, said there had been a reduction in Australia in breast cancer mortality in the past 15 years.
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"What we do know is that screening saves lives," he told AAP.
"We anticipate a lot of that is because of early detection."
Cancer Council Australia chief executive Professor Ian Olver told AAP the risk of overdiagnosis associated with screening did not outweigh the benefits.
"Women should be aware of the possibility of overdiagnosis, but of course will not be able to know whether this applies to their cancer or not," he said.
The review was published online on Tuesday in the journal Lancet.