One-third of women who are given information about the potential for overdiagnosis through the National Health Services (NHS) breast screening programme may not fully understand the risks involved, according to new research.

In a survey of approximately 2,200 women, Cancer Research United Kingdom (UK) scientists at University College London (UCL) found that 64% felt they fully understood the information given about overdiagnosis, which is the chance that screening will pick up cancers that would never have gone on to cause any harm.

However, information about overdiagnosis has only been included in the NHS breast screening invitation leaflets since late 2013. So, overdiagnosis is likely to be a new concept for many people.

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Yet despite uncertainty over the information they were given, intentions to attend breast screening remained high, with only 7% of women saying they would be less likely to attend screening after receiving the overdiagnosis information. On the other hand, 4% of women said they would be more likely to attend screening after receiving the information. The study was published in the British Journal of Cancer (2014; doi:10.1038/bjc.2014.482).

“While there is clearly room for improvement, the information leaflet does appear to help some women make a decision about whether or not to have breast screening,” said study author Jo Waller, PhD, a researcher at the Health Behaviour Research Centre at UCL. She added, “But the study found that many women still struggle to understand the balance of benefits and harms linked to breast screening, so we need to find better ways to communicate the risks as well as the benefits.”

Overdiagnosis happens because some breast cancers grow so slowly that it would take more than a lifetime for them to threaten a woman’s health. For every life that is saved through screening, researchers estimate that breast cancer will be overdiagnosed in approximately three women, however; currently there is no way to tell the difference between life-threatening cancers and cancers that are overdiagnosed, either at diagnosis or after treatment.

“We think it’s vitally important for women to have clear information about breast screening, the balance of benefits and harms and the fact that they could be diagnosed with and treated for a cancer that might not have caused them harm,” said Sara Hiom, Cancer Research UK’s director of early diagnosis. “We are committed to providing quality information that can help women understand the harms and benefits of breast screening, and research like this can help us refine the information we offer to be sure that it is as helpful and understandable as possible.