An independent review published in The Lancet today concludes that breast cancer screening prevents about 1,300 cancer deaths a year but it also leads to around 4,000 women having unnecessary treatment.
It is the first time there has been a quantified study of the problem of "over-diagnosis" and controversy has been growing over whether women are being fully informed before receiving invasive treatment as a result of their screening.
Today presenter John Humphrys spoke to two women who had very different reactions to the similar treatment that they received for their breast cancer.
Myriam Pryke explained that she had breast screening which resulted in two operations that she was "very reluctant" to have.
She added that she would not have had the screening or surgery if she had known that she "would have had to face the possibility of mutilating surgery only to discover that I didn't have cancer at all".
She expressed how a consultant had made her feel "under the threat of death", giving her no real option but to have surgery.
"I was railroaded," she said.
Diane Dally had a very different experience.
She went to get a screening reluctantly after initially turning down the invitation, doctors discovered she had cancer and she explained she was very glad she had treatment: "If I hadn't had it I think I would have ended up in a psychiatric hospital."
Professor Sir Mike Richards, the national cancer director at the Department for Health, said the report will provide "clarity" for patients.
"We can now present balanced information to the public so that when we're inviting them for screening, we can show both the pros and the cons in a fair manner."
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