© 2001 by Oxford University Press
Journal of the National Cancer Institute, Vol. 93, No. 5, 396,
March 7, 2001
© 2001 Oxford University Press
CORRESPONDENCE |
Re: Canadian National Breast Screening Study-2: 13-Year Results of a Randomized Trial in Women Aged 50–59 Years
Correspondence to: Steven A. Narod, M.D., FRCPC, The Centre for Research in Women's Health, University of Toronto, 790 Bay St., 7th Floor, Toronto, ON, Canada M5G 1N8 (e-mail: steven.narod{at}swchsc.on.ca).
Miller et al. (1) report on the most recent results of a randomized trial of breast screening in Canada. At 16 years after randomization, there were 107 deaths observed among women randomly assigned to receive annual mammography plus physical examination and 105 deaths among a similar number of women randomly assigned to receive an annual physical examination alone. The authors interpret this to mean that that the two methods of screening were equivalent—i.e., that annual physical examination by a trained professional is a viable alternative to annual mammography and should be available to women 50 years old or older. This message has also been highlighted by several media reports covering the publication of the trial results.
If this were a trial of mammography alone versus physical examination alone, this conclusion would be rational. However, if mammography and physical examination were equivalent (but not identical), I would expect the combination of the two to outperform either modality alone. In fact, the combination of mammography plus physical examination outperformed physical examination alone by every measure—except death. The tumors in the mammography arm were smaller, on average, than those detected in the physical examination arm and were more likely to be lymph node negative. Miller et al. present data showing that physical examination advanced the date of diagnosis by 1.5 years but that adding mammography advanced it further by 2.1 years. Surely, if physical examination were beneficial, then mammography must be more so. If early detection enhances the prospect of cure, a lead time of 3.6 years must be preferable to a lead time of 1.5 years. But this was not found to be the case. The rational interpretation of this dataset is not that the two screening methods were equivalent, but that neither was effective. I believe that researchers should now devote their attention to understanding why this is the case and should pay greater attention to advancing primary prevention.
REFERENCE
1
Miller AB, To T, Baines CJ, Wall C. Canadian National Breast Screening Study-2: 13-year results of a randomized trial in women aged 50–59 years. J Natl Cancer Inst 2000;92:1490–9.
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