Breast cancer screening reduces the number of deaths from the disease by 28%, new research suggests.
For every 368 women who are invited to have a mammogram, one death is prevented, the study claims.
Researchers from Norway set out to evaluate the effectiveness of modern mammography screening by comparing the effects on breast cancer mortality among screened and unscreened women.
The study, published on bmj.com, analysed data from all women in Norway aged 50 to 79 between 1986 and 2009 - the period in which the mammography screening programme was gradually rolled out across the country.
They analysed more than 15 million “person years” and observed breast cancer deaths among 1,175 of the women who were diagnosed after receiving an invitation to screening and in 8,996 of the women who were not invited.
After adjusting for various factors they estimated that invitation to mammography screening was associated with a 28% reduced risk of death from breast cancer.
“Women invited to screening in the Norwegian mammography screening programme were at a 28% lower risk of death from breast cancer than women who had not (yet) been invited,” the authors wrote.
“368 women aged 50-69 would need to be invited to biennial mammography screening to prevent one death from breast cancer during their lifetime.”
But an accompanying editorial says that the benefits of breast screening are “modest at best”.
The authors, from the University of Washington School of Medicine in Seattle and the University of North Carolina, called for women to be given more “balanced information” about the benefits and harms of breast screening.
“The new cohort study from Norway adds important information to a growing body of observational evidence estimating the benefits and harms of screening,” they wrote.
“The Norwegian study largely confirms what is already known: the benefits of screening mammography are modest at best.
“While the benefits are small, the harms of screening are real and include over-diagnosis, psychological stress, and exorbitant healthcare costs.
“So how can women be helped to make informed decisions about screening? Unfortunately they are rarely presented with balanced information.”
Commenting on the research, Baroness Delyth Morgan, chief executive of the charity Breast Cancer Campaign, said: “This study adds to existing evidence that confirms that breast screening saves lives. Diagnosing breast cancer quickly is vital, as the earlier breast cancer is diagnosed and treated, the greater the chances of survival.
“An independent review on breast screening in 2012 concluded that breast screening does save lives but also noted the risk of overdiagnosis as a result of screening. It’s therefore welcome that women are now receiving more detailed information in the form of the new breast screening leaflet to support them to make an informed decision about whether to attend screening.
“12,000 women sadly still die from breast cancer every year, which is why we have launched our campaign ‘Spread the word’, to ensure we continue the fight against breast cancer.”
Sally Greenbrook, senior policy officer at Breakthrough Breast Cancer, added: “Breakthrough Breast Cancer believes that screening saves lives but we understand that this is a confusing area and it is essential that women have access to balanced information about the risks and benefits of screening.
“This is why we developed our online breast screening tool which provides a balanced view of breast screening to allow women to decide for themselves whether or not to attend screening. This is available at www.breastscreeningfacts.org.”