Breast cancer screening is back in the headlines following the publication of a new paper in the British Medical Journal.

The paper was written by Danish researchers who have previously published work critical of the way women are given information about the balance of risks and benefits. They believe that women aren’t given sufficient information on the possible risks; and that these risks are underestimated.

Their new analysis suggests that as many as a third of women who receive treatment for breast cancer following screening, are treated unnecessarily as their cancer may not have gone on to cause them any harm.

This is a controversial finding. Previous estimates had put the figure much lower – as low as one in twenty. But what do other experts make of the new figures?

Ask the experts

We asked Cancer Research UK’s screening expert Stephen Duffy, Professor of Cancer Screening at the Wolfson Institute of Preventative Medicine, what he made of the findings. Here’s what he had to say:

“These results are not convincing for a number of reasons, but perhaps the most important is that the analysis does not take account of other effects on breast cancer incidence, such as use of hormone replacement therapy.

“Also, when screening takes place, cancers are diagnosed several years before they would have arisen clinically. Because this study does not observe incidence for a long enough period after screening started, it does not give a reliable estimate of how many tumours are overdiagnosed and how many are simply diagnosed earlier.

“There have been other studies which analysed the cancer incidence data more thoroughly and estimated much lower rates of overdiagnosis. For example, Waller’s study took into account hormone replacement therapy and its effect on incidence and found an overdiagnosis rate of one tumour in eight, rather than the one in three claimed by this study. Our own analysis from the randomised screening trials found rates of one in twenty.

“We therefore do not find the results of this study to be credible. Women should not be put off breast screening, which saves over a thousand lives a year in the UK.”

So despite the alarming headlines, this issue isn’t black and white. There’s still disagreement amongst experts about how important ‘overdiagnosis’ is in the case of breast cancer screening.

While the exact size of the risk of being treated unnecessarily is being debated, what’s not in doubt, however, is that thousands of women owe their lives to screening. The benefit of mammography, in terms of lives saved, is estimated to be in the order of 1,000 lives saved per year, as Professor Duffy noted.

How to make sense of this? It’s a tricky one. An editorial in the same issue of the BMJ has this inight:

“Mammography is one of medicine’s “close calls”—a delicate balance between benefits and harms—where different people in the same situation might reasonably make different choices.

“Mammography undoubtedly helps some women but hurts others. No right answer exists, instead it is a personal choice.”

Whatever the costs of screening – both human and financial – the fact that breast cancer screening saves lives should not be ignored.



Jorgensen, K., & Gotzsche, P. (2009). Overdiagnosis in publicly organised mammography screening programmes: systematic review of incidence trends BMJ, 339 (jul09 1) DOI: 10.1136/bmj.b2587