Breast cancer screening leads to thousands of women undergoing unnecessary treatment despite saving lives, according to an independent review.
The official study found that as many as 4,000 women in Britain receive therapy for non-life threatening forms of the disease every year because of overdiagnosis.
But it revealed that about 1,300 lives are saved by mammography.
The NHS Breast Cancer Screening Programme was launched in the UK in 1988 and invites all women aged between 50 and 70 to screening every three years.
There has been an ongoing debate about the benefits and harms of screening for the past 10 years, prompting the Government and charity Cancer Research UK to last year launch a review of the controversial programme.
An independent panel led by University College London's Professor Sir Michael Marmot was tasked with analysing data from screening trials from a number of countries over recent decades.
Its report, published in The Lancet, concludes that screening reduces breast cancer mortality but that some overdiagnosis occurs. It found that for every life saved, three women were overdiagnosed.
The panel said:
Professor Sir Mike Richards, National Cancer Director, added:
Dr Harpal Kumar, chief executive of Cancer Research UK, said: