Researchers have revealed that a third of breast cancers detected by screening may actually be harmless.
Some women undergo unnecessary treatment for cancers that are unlikely to spread or kill them, according to data from the UK, Australia, Canada, Norway and Sweden.
Often the cancer regresses or remains dormant, while others grow so slowly that the patient dies of other causes first.
Writing in the BMJ, researchers from the Nordic Cochrane Centre in Denmark concluded that cancer screening programmes may lead to ‘overdiagnosis’.
They wrote: ‘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 experts examined data for women in England and Wales from between 1971 and 1999.