Dutch scientists had expected that if screening older women is effective, it would increase the numbers of advanced disease detected.
Instead, the researchers found an increase in overdiagnosis and overtreatment.
The upper age limit for the national breast screening programme was extended from women age 69 to 75 in the Netherlands, and guidelines in the country suggest screening women up to the age of 75.
However, there is no strong evidence that screening older women is effective, due to the rarity of women of the age group in clinical trials.
By tracking all new cases of invasive and non-invasive (in situ) breast cancer, diagnosed in this age group from 1995 up to 2011, using data from the Netherlands Cancer Registry the researchers found that new cases of early stage breast cancer among 70-75 year olds rose sharply after national screening was introduced, from 248.7 to 362.9 per 100,000 women.
But while there was a significant fall in the numbers of new cases of advanced breast cancer, the absolute decrease was small, dropping from 58.6 before, to 51.8 cases per 100,000 women after, the national screening programme was introduced.
Among 76-80 year olds, new cases of early stage disease fell slightly, but the numbers of new cases of advance breast cancer didn’t change.
Based on the figures, the researchers calculated that for every advanced stage cancer detected by screening among 70-75 year olds, around 20 “extra” and therefore “overdiagnosed” early stage cancers are picked up, which they describe as a “considerable proportion.”
Overdiagnosis and overtreatment are important, the researchers emphasise, because they can undermine quality of life, and because older people are more vulnerable to the side effects of breast cancer treatment. And they come with a potentially hefty price tag in return for little obvious health benefit, they point out.
“Instead of using mass screening, the decision to participate in the screening programme should be personalised, based on remaining life expectancy, breast cancer risk, functional status and patients’ preferences,” they conclude.
Dr Caitlin Palframan, head of policy at Breakthrough Breast Cancer, said: “It's very important we learn more about the benefits and risks for this particular age group before we decide whether to offer these women routine screening [in the UK].
“No conclusive results should be taken from this study, however, until we see the results from the comprehensive and well-designed UK age extension trial. This is a very large randomised controlled trial looking at the benefits and risks of screening women aged 70-73, the results of which will be directly applicable to UK women.
“Whilst we await these results, women over 70 who would like to be screened can make an appointment with their local screening service. It's important that they make their decision whether or not to go for screening with an understanding that we don't yet know all the benefits and risks of screening for this age group."
The full study is available to view on thebmj.com
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