The benefits of breast cancer screening have been overstated and it can lead to patients having unnecessary surgery and harmful treatment, a top medic has warned.
A study of women in Denmark found about a third of cases involved overdiagnosis and suggested screening was not associated with a reduction in the number of advanced tumours.
Commenting on the research Otis Brawley, chief medical officer of the American Cancer Society, said "considering all small breast cancer lesions to be deadly aggressive cancer is the pathology equivalent of racial profiling".
He said screening was important but warned of an over-reliance and suggested the focus should be on disease prevention through diet and exercise.
The study, published in the Annals of Internal Medicine, looked at Denmark's screening programme, which offered mammograms to women aged between 50 and 69, and compared incidences of tumours found in women of different age groups in screening and non-screening areas.
Dr Brawley said the findings highlighted the problem of overdiagnosis - where "diseases" that were never going to cause any problem were picked up.
But the findings were described as nothing new in the debate, by Paul Pharoah, Professor of Cancer Epidemiology, University of Cambridge, who said screening remained a personal choice.
He said: "Consequently this study should not influence women who are considering having a screening mammogram on whether or not screening is the right thing for them.
"Randomised trials have shown that mammography reduces breast cancer mortality by a small amount, but this comes at the cost of increasing the number of women diagnosed and treated for breast cancer (so called overdiagnosis and overtreatment) so that some women will have unnecessary surgery and/or radiotherapy.
"Whether or not the benefit is worth the harm is an individual decision and different women will make different choices."