In the first comprehensive review of European breast cancer screening programs, scientists found that for every 1,000 women aged 50 to 69 screened every two years, between seven and nine lives are saved.

But in a finding likely to add to an already fierce international debate about the merits of routine screening for cancer, they also found that in the same group, four women would be "over-diagnosed" - when screening picks up a tumor that would never have presented a problem.

Stephen Duffy, professor of cancer screening at Queen Mary, University of London and one of two lead researchers on the study said the harm caused by over-diagnosis in the few women was clearly outweighed by the reduction in cancer deaths.

"(This review) reports results from screening millions of women, and confirms that the screening services are delivering the benefits expected from the research studies conducted years ago," he said as the research was published in the Journal of Medical Screening on Thursday.

"In particular it is good news that lives saved by screening outweigh over-diagnosed cases by a factor of two to one."

Over-diagnosed" breast cancers are tumors diagnosed during screening which would never have given rise to any symptoms during a woman's lifetime and would not have been diagnosed had she not been screened.

That can lead to women undergoing unnecessary and invasive treatment and suffering the physical and psychological impact of a breast cancer diagnosis that would otherwise not have come up.

The researchers also found that for every 1,000 women screened, 170 women would have at least one recall for a non-invasive assessment before a negative result could be confirmed, and 30 women would have at least one recall for an invasive procedure, such as a biopsy, before getting a negative result.

These types of results are called "false positives" and can cause stress and anxiety until a negative result is confirmed.

The issues of over-diagnosis and false positives were at the heart of rows among cancer patients and specialists in Europe and the United States which blew up in 2009 when American health officials questioned the value of routine mammograms for women at age 40 and suggested raising the annual screening age to 50.

Nordic scientists then published a study in 2010 which found no evidence that screening women for breast cancer has any effect on death rates and said it was "time to question whether screening has delivered the promised effect".

Worldwide, breast cancer is the most common cancer among women and around 1.38 million women were diagnosed it in 2008, according to the World Health Organisation's Globocan database.

In Europe, including non-European Union (EU) countries, 425,000 new cases of breast cancer were diagnosed in 2008 and 129,000 European women died of the disease.

For this latest study, the European Screening Network (EUROSCREEN) working group with members from nine European countries where screening programs have been assessed reviewed estimates of benefit in published studies in terms of cancer deaths prevented, and the major harms such as over-diagnosis.

It also reviewed the organization, participation rates and performance parameters of 26 screening programs in 18 countries involving 12 million women between 2001 and 2007.

Eugenio Paci, director of the Cancer Prevention and Research Institute in Florence, Italy and the co-lead researcher on the project, said the aim was to weigh up "the pros and cons of breast cancer screening" to ensure "women are fully aware of the chief benefits and harms and can make a fully informed choice" about whether to agree to be screened.

"There has been quite a lot of discussion recently over the worth of breast cancer screening," he said. "For this reason it is timely that the international group of experts has assessed the impact...and has found that it is contributing to the reduction in deaths from the disease."

He said the review's conclusions should be communicated to women in Europe and called for health authorities to improve communication with women and make the information "more accessible, relevant and comprehensible."

(Editing by Jane Merriman)

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