A study from Denmark published on bmj.com today finds no effect of the Danish screening programme on breast cancer deaths.
Similar results have been seen in other countries, including the UK, leading the authors to question whether screening has delivered the promised effect on breast cancer mortality.
A 2005 study suggested that screening had reduced breast cancer deaths by 25% in Copenhagen. But Karsten Jørgensen and Peter Gøtzsche from the Nordic Cochrane Centre in Copenhagen, together with Per-Henrik Zahl from Folkehelseinstituttet in Oslo, identified important problems in this study and decided to undertake a more comprehensive analysis of the data.
They compared annual changes in breast cancer deaths in two Danish regions offering publicly organised screening programmes (Copenhagen and Funen county) with non-screened regions across the rest of Denmark.
Their analysis covered 10 years after screening could have had an effect on breast cancer mortality. For comparison, they also looked at the 10-year period before screening was introduced.
Data for each area were divided into three age bands. Women aged 55-74 years, who could benefit from screening, and women aged 35-55 years and 75-84 years, who were largely unaffected by screening.
They found that in women who could benefit from screening (55-74 years) breast cancer mortality declined by 1% per year in the screened areas and by 2% per year in the non-screened areas. In women too young to benefit from screening (35-54 years), breast cancer mortality declined by 5% per year in the screened areas and by 6% per year in the non-screened areas during the same period.
For the older age groups (75-84 years), there was little change over time both in screened and non-screened areas.
"We were unable to find an effect of the Danish screening programme on breast cancer mortality," conclude the authors. "The reductions in breast cancer mortality we observed in screening regions were similar or less than those in non-screened areas and in younger age groups, and are more likely explained by changes in risk factors and improved treatment than by screening mammography."
"Our results are similar to what has been observed in other countries with nationally organised programmes. We believe it is time to question whether screening has delivered the promised effect on breast cancer mortality," they add.