The report took in data from 40,000 Norweigan women, and the conclusion is that between 15% and 25% of the cancers found via screening would not have gone on to be fatal or cause any symptoms. As a result, many women who underwent surgery, radiotherapy or chemotherapy did so unnecessarily.
Academics at the Harvard School of Public Health conducted the research, searching through records of women in Norway screened between 1996 and 2005. The data showed that one in every 2,500 women screened were saved, but six to ten were overdiagnosed.
Researcher Dr Mette Kalager, who worked on the study, said, "Radiologists have been trained to find even the smallest of tumours in a bid to detect as many cancers as possible to be able to cure breast cancer.
"However, the present study adds to the increasing body of evidence that this practice has caused a problem for women - diagnosis of breast cancer that wouldn't cause symptoms or death."
This new evidence follows the announcement last October that a review into cancer screening in the UK is underway. Prof Mike Richards, who is leading the review, said his worries “include the current state of the evidence relating to the benefits and harms of breast screening; how this information is communicated to women in order to promote informed choice; and the process by which decisions on screening are made in this country, including my own role.“I welcome this opportunity to discuss all these issues.”