BMJ  2005;331:350-351 (6 August), doi:10.1136/bmj.331.7512.350-b

Letter

Model of outcomes of screening mammography

Information needs to support informed choices

EDITOR—Barratt et al report that for every 1000 women screened from the age of 50 over 10 years, two fewer will die from breast cancer and 13 more will be diagnosed with breast cancer (corresponding to 63% more cancers, which mostly constitute overdiagnosis).¹ Similarly, we found that for every woman who has her life prolonged, five healthy women, who would not have received a breast cancer diagnosis in their lifetime if there had not been screening, will be converted into cancer patients unnecessarily.²

However, it is important to inform women that the often used estimate of 25-30% for the survival benefit is uncertain and rather optimistic.^{2 3} Barratt et al even used 37% since they adjusted their estimate of 25% for non-compliance. This procedure is doubtful since, as noted by two of the investigators in the screening trials, women who refuse to be screened have a worse prognosis, presumably because some of them are afraid of having a suspicion of breast cancer confirmed.⁴

These women also have a much higher death rate from all causes.⁴ We disagree that one can equate two fewer women who will die from breast cancer with two fewer who will die from any cause.¹ An effect of screening on all-cause mortality has not been shown.^{2 3} Breast cancer mortality is an unreliable outcome that is biased in favour of screening⁴; and the extra treatment because of overdiagnosis would be expected to lead to excess mortality in the screened group.⁵

pcg{at}cochrane.dk
Nordic Cochrane Centre, Rigshospitalet, Department 7112, Blegdamsvej 9, DK-2100 Copenhagen, Denmark

Nordic Cochrane Centre, Rigshospitalet, Department 7112, Blegdamsvej 9, DK-2100 Copenhagen, Denmark

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Competing interests: None declared.

References

1. Barratt A, Howard K, Irwing L, Salkeld G, Houssami N. Model of outcomes of screening mammography: information to support informed choices. BMJ 2005;330: 936. (23 April.)[Abstract/Free Full Text]
2. Olsen O, Gøtzsche PC. Systematic review of screening for breast cancer with mammography, 2001. http://image.thelancet.com/lancet/extra/fullreport.pdf (accessed 8 Jan 2004).
3. Humphrey LL, Helfand M, Chan BK, Woolf SH. Breast cancer screening: a summary of the evidence for the U.S. Preventive Services Task Force. Ann Intern Med 2002;137: 347-60.[Abstract/Free Full Text]
4. Gøtzsche PC. On the benefits and harms of screening for breast cancer. Int J Epidemiol 2004;33: 56-64.[Free Full Text]
5. Early Breast Cancer Trialists' Collaborative Group. Favourable and unfavourable effects on long-term survival of radiotherapy for early breast cancer: an overview of the randomised trials. Lancet 2000;355: 1757-70.[CrossRef][ISI][Medline]

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Relevant Article

Model of outcomes of screening mammography: information to support informed choices

Alexandra Barratt, Kirsten Howard, Les Irwig, Glenn Salkeld, and Nehmat Houssami
BMJ 2005 330: 936. [Abstract] [Full Text] [PDF]