Falling breast cancer death rates have little to do with breast screening but are down to better treatment and health systems, scientists said on Friday, in a study likely to fuel a long-running row over the merits of mammograms.

Researchers analyzed data from three pairs of countries in Europe and found that although breast cancer screening programs had been introduced 10 to 15 years earlier in some areas than in others, declines in death rates were similar.

The findings suggest that “improvements in treatment and in the efficiency of healthcare systems may be more plausible explanations” for falling deaths rates from breast cancer, they wrote in a study in the British Medical Journal.

World Health Organization (WHO) data show that deaths from breast cancer are decreasing in the United States, Australia, and most Nordic and western European countries but breast screening is a hot topic among experts who disagree about whether nationwide mammogram programs do more harm than good.

The fear among some is that over-diagnosis - when screening picks up tumors that would never have presented a problem - may mean many women are undergoing unnecessary radical treatment, suffering the physical and psychological impact of a breast cancer diagnosis that would otherwise not have come up.

But sweeping changes in U.S. guidelines two years ago that scaled back recommendations on breast screening caused an uproar among patient and doctors groups who said they put women at risk. That was swiftly followed by two conflicting European studies which further fueled the row.

The first, by Danish scientists, found that breast cancer screening programs of the type run by health services in Europe, the United States and other rich nations do nothing to reduce death rates from the disease, while the second, by a British team, found “substantial and significant reduction in breast cancer deaths” due to screening.

Then last month, researchers who conducted the longest ever breast cancer screening said it showed that regular mammograms prevent deaths from breast cancer, and that the number of lives saved increases over time.

Every year, breast cancer kills around 500,000 people globally and is diagnosed in close to 1.3 million people.

For this study, researchers from Britain, France and Norway used WHO data to compare trends in breast cancer death rates within three pairs of countries - Northern Ireland versus Republic of Ireland, the Netherlands versus Belgium and Flanders, and Sweden versus Norway.

Each pair had similar healthcare services and similar levels 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 team, lead by Philippe Autier of the International Prevention Research Institute in Lyon, France, said they expected that reductions in breast cancer death rates would show up earlier in countries where screening was introduced sooner, but their analysis in fact showed little difference.

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

“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,” Autier’s team wrote.

“This is in sharp contrast with the temporal difference of 10 to 15 years in implementation of mammography screening and suggests that screening has not played a direct part in the reductions of breast cancer mortality.”

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By Kate Kelland

LONDON