Published 21 July 2009, doi:10.1136/bmj.b2922
Cite this as: BMJ 2009;339:b2922

Letters

Breast screening

Breast screening saves lives

The first 150 words of the full text of this article appear below.

Godlee concludes incorrectly that our silence implies assent to Gøtzsche and colleagues’ views on the magnitude of the effect of mammographic screening in reducing breast cancer mortality.^{1 2 3 4}

In 1993 a meta-analysis of randomised trials showed a 24% reduction in breast cancer mortality among all women aged 50-74 invited for screening,⁵ a result that has been generally accepted. This intention to treat analysis avoids selection bias, but at the cost of diluting the true estimate of the reduction in breast cancer mortality in screened women because about 22% of women declined screening but were included in the analysis. The true "on treatment" effect of screening must therefore be greater than 24% and would have been 31% assuming no selection bias. In the absence of evidence of strong selection bias, the effect is likely to be about 30%.

Without screening about 5% of women die from breast cancer. Screening performed over about . . . [Full text of this article]

¹ Wolfson Institute of Preventive Medicine, Barts and the London School of Medicine and Dentistry, London EC1M 6BQ

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