Scientists are trying to work out a final figure to tell women about mammography's rate of 'overdiagnosis' (medical-speak for seeing a cancer that isn't actually there), but getting consensus isn't likely any time soon.
Previous studies have suggested a rate of anything from 5 per cent to 50 per cent, while a UK independent panel in 2012 settled on a figure of 19 per cent. Whatever the actual number, these false results have led to unnecessary treatment, which is very distressing for the woman and her family.
Mammography has been adopted around the world as the standard screening programme for detecting breast cancer, and its acceptance was helped by early reviews that suggested it could reduce the rate of breast cancer deaths by 30 per cent.
Although there has been a steep increase in the detection of early breast cancer, the rates of advanced cancers have declined only very slightly if at all, which suggests that mammography is detecting low-risk or non-progressive breast cancers (such as DCIS), says Alexandra Barrett, professor of public health at Sydney University.
As 99 per cent of women with detected breast cancer go on to have chemotherapy, radiotherapy or breast removal, a false-positive rate of 20 per cent suggests that one-fifth of all cases are false-positives that nonetheless trigger unnecessary, invasive and distressing treatment, she says.
(Source: BMJ, 2015; 350: h867)