Too much mammography

Before being widely implemented, mammography screening was tested in randomised controlled trials in the 1960s to 80s. Meta-analyses of these trials showed a relative reduction in deaths from breast cancer of between 15% and 25% among women aged 50 to 69.1 2 3 Only the Canadian National Breast Screening Study showed no reduction in breast cancer mortality.1 2 3 This large randomised controlled trial compared physical breast examination with combined physical breast examination and annual mammography in women aged 40 to 59.1 2 3

In a linked paper (doi:10.1136/bmj.g366), Miller and colleagues present the results for up to 25 years of follow-up in the Canadian study.4 No difference in breast cancer mortality was observed between the mammography and control arms, whereas a significant excess incidence of invasive breast cancer was observed in the mammography arm, resulting in 22% overdiagnosis. This means that 22% of screen detected invasive cancers would not have reduced a woman’s life expectancy if left undetected.

The major strengths of this study include its randomised design, intense intervention with …