An international team of researchers from France, the UK and Norway found that better treatment and improving health systems are more likely to have led to falling numbers of deaths from breast cancer than screening.

The number of deaths from breast cancer is falling in many developed countries, but it is difficult to determine how much of that reduction over the past 20 years of mammography screening is due to earlier detection or to improved management.

From 1965 to 1980, cervical cancer mortality fell earlier and more strongly in Nordic countries that implemented nationwide screening programmes compared with those that delayed screening.

So the team used a similar approach to compare trends in breast cancer mortality within three pairs of European countries -- Northern Ireland versus Republic of Ireland, the Netherlands versus Belgium and Flanders, and Sweden versus Norway.

The researchers expected that a reduction in breast cancer mortality would appear sooner in countries with earlier implementation of screening.

Countries of each pair had similar healthcare services and level of risk factors for breast cancer mortality, but were different in that mammography screening was implemented about 10 to 15 years later in the second country of each pair.

The researchers studied data from the World Health Organisation (WHO) mortality database on cause of death covering the period 1980 to 2006 and data sources on risk factors for breast cancer death, mammography screening, and cancer treatment.

Results showed that from 1989 to 2006, deaths from breast cancer fell by 29% in Northern Ireland and 26% in the Republic of Ireland; by 25% in the Netherlands, 20% in Belgium and 25% in Flanders; and by 16% in Sweden and 24% in Norway.

These trends in breast cancer mortality rates varied little between countries where women had been screened by mammography for a considerable time compared with those where women were largely unscreened during that same period, say the authors. Furthermore, the greatest reductions were in women aged 40-49, regardless of the availability of screening in this age group.

They conclude: "The contrast between the time differences in implementation of mammography screening and the similarity in reductions in mortality between the country pairs suggest that screening did not play a direct part in the reductions in breast cancer mortality."

They add: "Improvements in treatment and in the efficiency of healthcare systems efficiency may be more plausible explanations."