Concerns have been raised that breast cancer screening might lead to some women undergoing unnecessary treatment.
Breast screening may produce false positives
Researchers looked at international studies on half a million women.
They found that for every 2,000 women screened over a decade, one will have her life prolonged, but 10 will have to undergo unnecessary treatment.
UK experts said women over 50 should go for their breast checks, but a screening pioneer raised doubts about the NHS programme's future.
The report, published in the Cochrane Library, involved a review of breast cancer research papers from around the world.
The scientists found mammograms did reduce the number of women dying from the disease.
But they also discovered it was diagnosing woman with breast cancer who would have survived without treatment, meaning they were undergoing unnecessary chemotherapy, radiotherapy or mastectomies.
About a fifth of cancers picked up by screening are in the milk ducts of the breast.
Some of these cancers will progress while others will not - but there is no way of predicting what will happen.
This means women and doctors have to decide whether or not to risk doing nothing, or go ahead with treatment which might be unnecessary.
They also revealed a further 200 women out of every 2,000 experienced distress and anxiety because of false positives - a result that indicated a cancer was present but was later found to be wrong.
Lead researcher Dr Peter Gotzsche, of the Nordic Cochrane Centre, said: "Women invited to screening should be fully informed of both benefits and harm.
"When screening advocates and their organisations produce information materials, they generally emphasise the benefits and omit information on the major harms.
"This needs to be corrected to ensure that women can give genuinely informed consent before joining a screening programme."
In 2001, the same authors concluded there was no convincing evidence that screening programmes reduce mortality from the disease.
Michael Baum, professor of surgery at University College London who set up one of England's first screening programme in 1987, told the Daily Telegraph: "This latest evidence shifts the balance even further towards harm and away from benefits.
"If this report stands up, the NHS screening programme should be referred to the National Institute for health and Clinical Excellence to decide whether it should be closed down."
But a spokesman for the Department of Health said that, as mammography was an accepted, evidence-based technology, it would not be appropriate to refer the screening programme to NICE."
And Professor John Toy, medical director of Cancer Research UK, said: "Researchers in the field all agree that breast screening saves lives although they differ in their views about the balance of the pros and cons.
"Benefits need to be balanced against any disadvantages, as is the case with all medical treatments.
"Certainly women invited for screening should be made aware of both potential benefits and downsides - such as possible initial mis-diagnosis.
"But overall we continue to encourage UK women to participate in the NHS Breast Screening Programme."
Jeremy Hughes, chief executive of Breakthrough Breast Cancer said: "When early changes are picked up by screening it is not currently possible to predict whether or not they will progress and so treatment is usually offered to prevent breast cancer from developing.
"It's important women are given clear information about their treatment options. Early detection saves lives. Women over 50 should not be discouraged from taking up their screening appointments."
And Julietta Patnick director of the NHS Cancer Screening Programmes said: "The programme saves 1,400 lives every year. Women who are screened are also less likely to have a mastectomy than those who are not screened.
"For lives to be saved breast screening must detect cancers in the early stages. The benefits of breast screening far outweigh the risks and I would strongly encourage all women to make an informed choice to attend for screening when invited."