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Possible net harms of breast cancer screening: updated modelling of Forrest report

BMJ 2011; 343 doi: 10.1136/bmj.d7627 (Published 8 December 2011) Cite this as: BMJ 2011;343:d7627


Objective To assess the claim in a Cochrane review that mammographic breast cancer screening could be doing more harm than good by updating the analysis in the Forrest report, which led to screening in the United Kingdom.

Design Development of a life table model, which replicated Forrest’s results before updating and extending them with data from relevant systematic reviews, trials, and other models based on purposive literature searches.

Participants Women aged 50 and over invited for breast cancer screening.

Main outcome measures Quality adjusted life years (QALYs), combining life years gained from screening with losses of quality of life from false positive diagnoses and surgery. 

Results Inclusion of the effects of harms reduced the updated estimate of net cumulative QALYs gained after 20 years from 3301 to 1536 or by more than half. The best estimates from the Cochrane review generated negative QALYs for the first seven years of screening, 70 QALYs after 10 years, and 834 QALYs after 20 years. Sensitivity analysis showed these results were robust to a range of assumptions, particularly up to 10 years. It also indicated the importance of the level and duration of harms from surgery.

Conclusions This analysis supports the claim that the introduction of breast cancer screening might have caused net harm for up to 10 years after the start of screening. 


The Forrest report in 1986,1 which led to the introduction of mammographic breast screening in the United Kingdom, analysed the costs and benefits in terms of quality adjusted life years (QALYs). One of the earliest uses of QALYs to guide policy, it suggested that screening would reduce the death rate from breast cancer by almost one third with few harms and at low cost (for details see appendix on bmj.com).

The key data used in the Forrest report were drawn from two randomised trials, the Swedish two counties trial2 and the Health Insurance Plan (HIP) New York trial.3 The Forrest report claimed that overdiagnosis was not a problem, based on the New York trial, but noted that the Swedish trial found possible overdiagnosis of 20%. It stated that “further follow up is required to find out whether this excess persisted.” We have updated the Forrest report’s estimates for mortality and extended them to include the effects of false positives and overdiagnosis.

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