One in three breast cancers 'harmless'
Updated on 10 July 2009
One in three breast cancers detected by screening may actually be harmless, new research has shown.
Data from the UK, Canada, Australia, Sweden and Norway suggests some women undergo unnecessary treatment for cancers that are unlikely to kill them or spread.
Some cancers grow so slowly that the patient dies of other causes first, or the cancer remains dormant or regresses.
Researchers from the Nordic Cochrane Centre in Denmark said today that cancer screening programmes could lead to "overdiagnosis".
Writing in the British Medical Journal (BMJ), they said: "Screening for cancer may lead to earlier detection of lethal cancers but also detects harmless ones that will not cause death or symptoms.
"The detection of such cancers, which would not have been identified clinically in someone's remaining lifetime, is called overdiagnosis and can only be harmful to those who experience it.
"As it is not possible to distinguish between lethal and harmless cancers, all detected cancers are treated. Overdiagnosis and overtreatment are therefore inevitable."
The authors pointed to autopsy data which has shown that about 37 per cent of women aged 40 to 54 "who died from causes other than breast cancer, had lesions of invasive or non-invasive cancer at autopsy".
About half of these lesions would have been picked up in screening and some would have been treated, they said.
Meanwhile, statistics have shown that deaths from three of the most common cancers - breast, bowel and lung - have fallen to their lowest level since 1971.
UK breast cancer deaths among women peaked in 1989 at 15,625 but dropped 36 per cent to 11,990 in 2007, according to the data, from Cancer Research UK.
Bowel cancer deaths among both sexes peaked in 1992 at 19,598, but fell 31 per cent to 16,007 in 2007. And the number of men dying from lung cancer peaked in 1979 at 30,391 but dropped 53 per cent to 19,637 in 2007.
The number of people developing cancer is on the rise as people live longer than ever - but fewer people are dying from the disease partly due to improved screening and new and better treatments.
Deaths from lung cancer have also been falling as people give up smoking.
Cancer Research UK is now launching a new national TV advertising campaign to raise more money and increase awareness of the fight against cancer.
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