Alexandra Barrett, an epidemiologist at the University of Sydney, Australia, explains her view of breast screening in an article in Nature this month. ‘Because a screening mammogram is a snapshot in time, it is more likely to catch a slow growing cancer’, she writes. ‘Estimates vary, but I’m more likely to be over-diagnosed than to have my life saved — three to ten times more likely’. 1, 2.
This is because mammograms find small changes that would never affect a woman in her lifetime, even though these are called ‘cancers’. However, regular screening is far less likely to find the fast growing, dangerous cancers – which tend to become noticeable between screenings.
Perhaps incredibly, over-diagnosis leads to over-treatment; doctors do not know which of the ‘changes/cancers’ will cause a problem so they tend to treat them all, often with mastectomy. The physical and psychological effects of cancer treatments can be profound (including a lifelong risk of lymphoedema, a fairly common side effect not mentioned in this article) and a ‘cancer’ diagnosis can also label a family.
The Risks of Overdiagnosis, Barrett A. S104, Nature Vol 527, 19 November 2015.
1Marmot, M. G. et al. Lancet 380, 1778–1786 (2012).
2. Gøtzsche, P. C. & Jørgensen, K. J. Cochrane Database Syst. Rev. 2013,
Here are the remaining useful references given in the article:
Carter, J. L., Coletti, R. J. & Harris, R. P. Br. Med. J. 350, g7773 (2015).
Esserman, L., Shieh, Y. & Thompson, I. J. Am. Med. Assoc. 302, 1685–1692
Welch, H. G. & Black, W. C. J. Natl Cancer Inst. 102, 605–613 (2010).
Welch, H. G. & Passow, H. J. JAMA Intern. Med. 174, 448–454 (2014).
Hersch, J. et al. Lancet 385, 1642–1652 (2015).