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Harms from breast cancer screening outweigh benefits if death caused by treatment is included

BMJ 2013; 346 doi: http://dx.doi.org/10.1136/bmj.f385 (Published 23 January 2013)
Cite this as: BMJ 2013;346:f385

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  1. Michael Baum, professor emeritus of surgery, Division of Surgery and Interventional Science, University College London, London WC1E 6BT, UK
  1. michael{at}mbaum.freeserve.co.uk

Each new intake of medical students to my surgical “firm” started off with a tutorial where I posed a rhetorical question: “Why do we screen for cancer?” To which the inevitable answer would be, “To catch it early, sir.” Wrong. The question should be reframed, as “Does screening for cancer improve length or quality of life?” All other outcomes are surrogates.

The clinical trials of screening for breast cancer that informed the recent Marmot review1 made no attempt to measure quality of life, but a surrogate for that might be mastectomy rate in screened compared with unscreened populations. On that measure alone, screening fails: the hazard ratio for mastectomy of 1.2 favours the unscreened population.2

So, does screening improve length of life? Sadly, the Marmot committee chose to duck that one and rely on another surrogate outcome measure, cause specific mortality, with the rather lame excuse that the trials weren’t powered to detect any impact on all cause mortality. Well shame on them, I say. The ProtecT trial of prostate specific antigen screening for prostate cancer gives equal weight to cause specific and all cause mortality by accepting that overdiagnosis and overtreatment might lead to an increase in all cause mortality.3 Here I estimate the additional non-breast cancer deaths that might be the consequence of screening for breast cancer.

The CRC1 trial was published in the BMJ in 1989.4 Patients were randomised to mastectomy with or without radiotherapy. This cohort of 2800 women was recruited contemporaneously with those in the old randomised trials of screening by mammography. Note in figure 1 of this paper that the 10 year survival was about 55%. Also, after …

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