Research published in the British Journal of Cancer (BJC) says that a third of women who are given information about the chance of 'overdiagnosis' through the NHS breast screening program may not fully understand the risks involved.
In a survey of around 2,200 women, Cancer Research UK scientists at University College London (UCL) found that 64 per cent felt they fully understood the information given about overdiagnosis - the chance that screening will pick up cancers that would never have gone on to cause any harm - by the National breast screening programme.
But information about overdiagnosis has only been included in the NHS breast screening invitation leaflets since late 2013, meaning that overdiagnosis is likely to be a new concept for many people.
Yet despite uncertainty over the information they were given, intentions to attend breast screening remained high, with only seven per cent of women saying they would be less likely to attend screening after receiving the overdiagnosis information. On the other hand, four per cent of women said they would be more likely to attend screening after receiving the information.
Study author, Dr Jo Waller, a researcher at the Health Behaviour Research Centre at UCL, said: "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."
"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 around three women will be overdiagnosed with breast cancer, although there is presently no way of telling the difference between life-threatening cancers and cancers that are overdiagnosed, either at diagnosis or after treatment.
Sara Hiom, Cancer Research UK's director of early diagnosis, said: "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."
"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."
"The concept of overdiagnosis is still very new for a lot of women because it has only been included in the NHS leaflets for a year. We hope that over time, people's understanding of this concept will increase as more and more women receive information explaining this risk of screening."
"Any woman invited for breast screening and worried about the risks of overdiagnosis can speak to our specialist cancer nurses on freephone 0808 800 4040."