An NHS trial is underway to assess the impact of extending the age range for the national breast cancer screening programme to include 71 to 73-year-olds, as well as women aged 47-49.
But researchers investigating an extension of a programme in the Netherlands to include women up to age 75 found only a modest impact on preventing advanced cases, with high rates of overdiagnosis of early stage disease.
They warned that screening this age group could harm more patients than it benefits and greatly increase treatment costs.
The researchers called for personalised screening based on risk factors for women in this age group, rather than mass screening, to avoid harms associated with overdiagnosis.
The study from Leiden University Medical Centre, published in The BMJ, looked at 25,500 breast cancer cases between 1995 and 2011. This timeframe included the period 1998-2002, when the 70-75 screening programme ran. Early data from the study were presented at the European Breast Cancer conference in March.
Early stage breast cancer cases rose sharply in the 70-75 age group after screening began, from 248.7 to 362.9 cases per 100,000 women.
Although advanced breast cancer cases fell, the reduction was small, from 58.6 to 51.8 cases per 100,000.
The researchers calculated that for each additional advanced cancer case picked up by screening, a further 20 'extra' early stage cancers were discovered, which count as overdiagnosed cases.
The results implied that mass screening in women aged 70-75 years 'leads to a considerable proportion of tumours that are overdiagnosed'.
They warned that overdiagnosis, and resulting overtreatment, can adversely impact quality of life and physical function in older women with breast cancer.
'No actual health benefits'
After a certain age, the adverse effects of screening may outweigh the benefits, while extra costs of treating overdiagnosed cancer 'could result in a tremendous increase in health expenditure as a result of the screening programme, with no actual health benefits', they said.
They wrote: '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.'
Study authors noted the ongoing NHS trial, which is being conducted by Cancer Research UK, adding: 'Until the results of this trial become available, we propose that routine breast cancer screening in women aged more than 70 years should not be performed on a large scale.'
More than a million women have so far taken part in the extended NHS screening programme trial.
Jessica Kirby, senior health information manager at Cancer Research UK, said: 'This study didn’t look at the number of deaths from breast cancer in screened or unscreened women, and the follow-up period may not have been long enough to be sure of detecting changes in the rates of advanced cancers, so it’s hard to draw firm conclusions about the effectiveness of breast screening in this age group.
'But we know that breast screening has both benefits and harms – it leads to overdiagnosis as well as saving lives from breast cancer – and women over 70 should be offered balanced information about the pros and cons of screening so they can make an informed decision about whether to take up screening or not.'