The common perception of mammography is that, by detecting breast cancer earlier than it would otherwise be, it saves women’s lives. However, there is quite some evidence to suggest that many women need to be screen for one life to be saved, and on top of this we have adverse effects such as over-diagnosis (the detection and treatment of breast cancers that would never have bothered a women during the natural course of her life if left undetected).
A new study casts fresh doubt on the effectiveness of mammography as a ‘life-saver’. It involved long-term follow-up of a group of about 90,000 women in Canada, half of whom had been selected for mammography (five mammograms over five years) or no mammography (but did receive at least one breast examination).
During the entire 25-year study, 3,250 women in the mammography group and 3,133 in the non-mammography group were diagnosed with breast cancer. Basically, in this setting, mammography did not improve breast cancer detection. But more importantly, deaths from breast cancer were virtually identical across the two groups. In other words, screening about 45,000 women for 5 years did not reduce their risk of breast cancer compared to breast examination.
This study also assessed over-diagnosis. According to the data, for every 424 women screened, one woman had a breast cancer detected that would not have bothered her if left undetected and untreated.
All-in-all not a great advert for mammography, and another piece of evidence that demonstrates that this practice has been vigorously promoted by some even though the evidence for it is not strong at all.
1. Miller AB, et al. Twenty five year follow-up for breast cancer incidence and mortality of the Canadian National Breast Screening Study: randomised screening trial. BMJ 2014; 348:g366