Breast screening curbs breast cancer deaths
BMJ Group News
A study from Norway adds to the research showing that breast cancer screening saves some lives, but debate continues about whether the number of women helped by screening outweighs the number harmed.
What do we know already?
The NHS has been offering breast screening with mammograms to women for more than 25 years. The goal of screening is to save lives by finding breast cancers early, when they are easier to treat.
There has been debate in recent years about whether the benefits of breast screening outweigh the possible harms. These harms include having a false screening result that suggests a woman may have breast cancer when she does not, or having unnecessary treatment for an early cancer found by screening that would never have caused problems in a woman’s lifetime.
Much of the controversy over breast screening comes from questions about how many lives breast screening actually saves. Early studies on breast screening found that it significantly reduced women’s chances of dying of breast cancer. However, in recent years researchers have questioned the reliability of these studies and also whether their findings still apply today. This is because treatments for breast cancer have improved considerably since these studies were done back in the 1970s and 1980s. So fewer women are now dying of breast cancer, perhaps making early detection through screening less important.
How was the new study done?
To explore the benefits of breast screening in light of improved breast cancer treatments, researchers turned to Norway. The Norwegian breast screening programme started fairly recently, rolling out gradually from 1995 to 2005. In the programme, all Norwegian women aged 50 to 69 years are invited to have breast screening every two years.
To estimate how many lives breast screening saves, the researchers looked at all the women in Norway who were aged 50 to 79 years between 1986 and 2009. This included women who had been diagnosed with breast cancer both before screening had started and after. Taking time of diagnosis into account, the researchers compared how likely women were to have died of breast cancer through to the end of 2009, based on whether they’d been invited for screening or not.
What does the new study say?
Women who were invited for screening were less likely to have died of breast cancer than women who were not invited, although the difference between the groups was fairly modest. Nearly 5 in every 10,000 women who’d been invited for screening died of breast cancer, compared with nearly 7 in every 10,000 women who’d not been invited.
The researchers estimated that one death from breast cancer was prevented for every 368 women invited for screening, and one death was prevented for every 280 women who actually attended screening.