For every breast cancer that is properly diagnosed by a mammogram, five are 'seen' that aren't actually there. These false diagnoses nonetheless result in surgery or a course of chemotherapy, a new study has found.
The study has been prepared for the Norwegian government, which must decide whether to keep the routine mammogram screening programme going. In 2013, Swiss authorities were recommended to end the nation's programme, while England was recommended to keep its in 2012.
Despite the high rate of false-positives, as an incorrect diagnosis is known, the Norwegian study concludes by recommending that the nation keeps its screening programme going. "The goal was to reduce breast cancer mortality rates by 30 per cent. Depending on how you look at it, our estimates show that this goal may have been reached. But it has taken a huge toll in the form of over-diagnosis," said Prof Roar Johnsen at the Norwegian University of Science and Technology, who prepared the report.
Even the rate of lives saved seems to vary enormously from study to study, with one suggesting that mammography has reduced the rate of breast cancer deaths by as little as 10 per cent, while, at the other extreme, another reckoned it had reduced deaths by 36 per cent.
But what wasn't in any doubt was the rate of false-positives that mammography has consistently produced. For every 27 women correctly diagnosed, 142 have a false-positive reading that results in surgery or chemotherapy. This unnecessary treatment adds to the country's health budget, which already spends NOK 574 m (UKlb45m) per screening round for women aged between 50 and 69.
(Source: Norwegian University of Science and Technology)