Research

Overdiagnosis in publicly organised mammography screening programmes: systematic review of incidence trends

BMJ 2009; 339 doi: http://dx.doi.org/10.1136/bmj.b2587 (Published 09 July 2009) Cite this as: BMJ 2009;339:b2587
  1. Karsten Juhl Jørgensen, researcher,
  2. Peter C Gøtzsche, director
  1. 1The Nordic Cochrane Centre, Rigshospitalet, Dept 3343, Blegdamsvej 9, DK-2100 Copenhagen, Denmark
  1. Correspondence to: K J Jørgensen kj{at}cochrane.dk
  • Accepted 30 January 2009

Abstract

Objective To estimate the extent of overdiagnosis (the detection of cancers that will not cause death or symptoms) in publicly organised screening programmes.

Design Systematic review of published trends in incidence of breast cancer before and after the introduction of mammography screening.

Data sources PubMed (April 2007), reference lists, and authors.

Review methods One author extracted data on incidence of breast cancer (including carcinoma in situ), population size, screening uptake, time periods, and age groups, which were checked independently by the other author. Linear regression was used to estimate trends in incidence before and after the introduction of screening and in older, previously screened women. Meta-analysis was used to estimate the extent of overdiagnosis.

Results Incidence data covering at least seven years before screening and seven years after screening had been fully implemented, and including both screened and non-screened age groups, were available from the United Kingdom; Manitoba, Canada; New South Wales, Australia; Sweden; and parts of Norway. The implementation phase with its prevalence peak was excluded and adjustment made for changing background incidence and compensatory drops in incidence among older, previously screened women. Overdiagnosis was estimated at 52% (95% confidence interval 46% to 58%). Data from three countries showed a drop in incidence as the women exceeded the age limit for screening, but the reduction was small and the estimate of overdiagnosis was compensated for in this review.

Conclusions The increase in incidence of breast cancer was closely related to the introduction of screening and little of this increase was compensated for by a drop in incidence of breast cancer in previously screened women. One in three breast cancers detected in a population offered organised screening is overdiagnosed.

Footnotes

  • We thank Alain Demers (Department of Epidemiology and Cancer Registry, CancerCare Manitoba) for supplying data for Manitoba, Per-Henrik Zahl (Folkehelseinstituttet, Oslo) for supplying data for Sweden and Norway, and Gilbert Welch for helpful comments on the manuscript.

  • Contributors: PCG and KJJ conceived the study, developed the methods, extracted data and carried out the analyses. KJJ did the searches, contacted authors, and wrote the first draft of the manuscript, which was revised by PCG. Both authors are guarantors.

  • Funding: None.

  • Competing interests: None declared.

  • Ethical approval: Not required.

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-commercial License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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