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© 2005 Oxford University Press
CORRESPONDENCE |
RESPONSE: Re: Efficacy of Breast Cancer Screening in the Community According to Risk Level
Correspondence to: Russell Harris, MD, MPH, Professor of Medicine, Sheps Center for Health Services Research, University of North Carolina School of Medicine, Chapel Hill, NC 27599 (e-mail: rharris{at}med.unc.edu).
I am pleased that Duffy et al. agree that the issue of effectiveness is the next important question for breast cancer screening. Unfortunately, they apparently misunderstood the underlying analysis in my editorial (1) and believe that I concluded that "screening has a less than 20% effect on mortality."
What I said was that the study by Elmore et al. raises, but does not resolve, important questions about the effectiveness of screening, one of which is whether effectiveness in real life may be less than efficacy in the randomized controlled trials. The real question is: Do we know what contribution breast cancer screening in the United States in 2005 is making to reducing mortality from breast cancer? The truth is that we do not know. I offered two reasons why screening may be having a smaller effect on mortality than one might predict from the results of randomized controlled trials, problems with implementation and changing context, and I suggested ongoing research to provide more information on the issue.
Duffy et al. refer to their previous article (2) as if it answers the issue of effectiveness. In that article, they draw the counterintuitive conclusion that screening in the community has an even greater effect on breast cancer mortality than that found in the carefully conducted randomized controlled trials. In their article, they made comparisons among nonrandomized groups of women who differed by age and by time period. Those groups, of course, differed in many ways other than only screening and treatment. Although a detailed critique of that article is beyond the scope of this letter, suffice it to say that the authors' attempts to adjust for such differences were insufficient. Their study—like that of Elmore et al.—raises issues but does not resolve them.
The effectiveness question will not go away soon.
REFERENCES
(1) Harris R. Effectiveness: the next question for breast cancer screening. J Natl Cancer Inst 2005;97:1021–2.
(2) Tabar L, Yen MF, Vitak B, Chen HHT, Smith RA, Duffy SW. Mammography service screening and mortality in breast cancer patients: 20-year follow-up before and after introduction of screening. Lancet 2003;361:1405–10.[CrossRef][Web of Science][Medline]
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J Natl Cancer Inst 2005 97: 1703.
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