Mammograms have played an insignificant role in falling breast cancer death rates in Europe, according to a study published Friday.
Three pairs of countries with similar access to treatment but varying levels of breast screening showed scant difference in the degree of mortality attributed to the disease, researchers reported.
The study, published online by the British Medical Journal, adds to a growing body of evidence suggesting that two decades of routine screening has yielded modest results at best.
A trio of scientists led by Philippe Autier of the International Prevention Research Institute in Lyon, France compared the mortality rates of otherwise similar health systems that began screening programs at least a decade apart.
In Northern Ireland, which began systematic mammograms in the early 1990s, the death rate among breast cancer patients dropped 29 percent from 1989 to 2006. In Ireland, mortality went down nearly as much, 26 percent, over the same period even though the country didn't set up regular screening until 10 years later.
The Netherlands and Belgium also showed a parallel drop in breast cancer mortality rates -- identical in the case of Dutch-speaking Belgium -- despite a lag time of about a decade in the implementation of screening programmes.
And in Sweden, which in 1986 pioneered systematic mammograms to detect the disease, the drop was only 16 percent, compared to 24 percent in Norway, which began to do so only in 2005.
The slim difference in mortality rates suggests that the decrease was caused by other factors, such as better treatment, the researchers said.
"Since we began studying the long-term effects on mortality, a lot of data has suggested that the impact is little to none," Autier told AFP.
"I am among those who pushed hard for systematic screening for breast cancer in the 1990s," he added.
"But now there are question marks and we have to provide answers, because we cannot continue to promote something that may not be very effective but which can lead to a certain number of false positives," where healthy women are diagnosed as having the disease, he said.
Not all researchers agree that new data show screening to have been of marginal utility.
"The improvement in the prognosis of breast cancer patients is a multi-factor phenomenon," said Jerome Viguier, head of detection and screening at France's National Cancer Institute.
"It is very difficult to distinguish between different evolutions that are complementary and move in parallel," he told AFP by phone.
Viguier also emphasised that reducing mortality -- even if it is the overarching objective of screening -- is not the only impact.
"The aim is also to intervene earlier in the disease so that treatment is less invasive, with less mutilation, and fewer scares," he said.
He also questioned the premise of the new study that the health care systems compared were similar enough to single out systematic screening as the only significant difference.
Some experts argue that the difficult decision of whether to screen -- involving trade-offs among non-comparable outcomes -- must be left to informed individuals.
Others say that physicians should continue to encourage women to undergo regular screening because even modest benefits trump potentially negative impacts.