RE: Mammography Screening and Risk of Breast Cancer Death: a Population-Based Case–Control Study, by S

Author Manuscript Published OnlineFirst on March 8, 2012; DOI: 10.1158/1055-9965.EPI-12-0033 Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.

N=396

Letter to the Editor

RE: Mammography screening and risk of breast cancer death: A population-based case–control study, by S. Otto and Colleagues, published in Cancer Epidemiology Biomarkers and Prevention on December 6th, 2011.

Philippe Autier, MD, and Mathieu Boniol, PhD International Prevention Research Institute, Lyon (France)

Correspondance Ph Autier, International Prevention Research Institute, 95 Cours Lafayette, F-69006 Lyon (France). [email protected]; www.i-pri.org.

Conflict of interest None to declare

Downloaded from cebp.aacrjournals.org on September 25, 2021. © 2012 American Association for Cancer Research. Author Manuscript Published OnlineFirst on March 8, 2012; DOI: 10.1158/1055-9965.EPI-12-0033 Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.

A case-control study in the Netherlands found that participation in

mammography screening reduced 49% the risk of dying from breast cancer by

49% (1). Cases were women who were diagnosed with breast cancer and died

from it. Controls were women who were still alive at the date of death of the case

and were breast cancer free at the date of breast cancer diagnosis of the case. We

believe that methodological limitations inherent to the case-control design

undermine the credibility of findings.

Despite the absence of financial barriers for participation in the Dutch mass-

screening program, in general, non-participating women are more deprived,

have more co-morbidities and have a higher risk of dying from breast cancer or

from other causes than women participating in screening (2,3). Hence, screening

participants and non-participants presents genuine differences in risk factors

associated with dying from breast cancer or from other causes.

Consequently, in the Otto et al. study (1), controls were more likely to be women

participating in screening simply because they were less likely to die from any

cause in the time interval between the breast cancer diagnosis and the breast

cancer death in the case. In addition, although a number of non-participants died

from breast cancer for reasons unrelated to screening (e.g., lower compliance to

treatments, higher prevalence of obesity), the case-control design implied that

these deaths were due to not having been screened (confounding by indication).

The method used to correct for the fact that women at higher risk to die from

breast cancer or from other cause would participate less more to screening (self-

selection) is based on a correction factor calculated as the relative risk of death

from breast cancer among non-participants compared with breast cancer

mortality rates before screening introduction (4). This method, however, leads to

biased results when applied to data collected during a period when breast cancer

mortality was decreasing, which was the case in many European countries after

1990 (5). For instance, the correction factor decreases with decreases in breast

cancer mortality in non-participants due to improved treatments. Mortality

reductions after 1990 are positively correlated with mortality rates that prevailed

in the 1980s (5). Therefore, the correction factor will decrease with increasing

mortality rates before screening commences. Furthermore, correction for self-

selection is unable to adjust for confounding by indication occurring after

screening introduction, for instance, imbalances in disease management between

participants and non-participants.

References

1. Otto SJ, Fracheboud J, Verbeek ALM, Boer R, Reijerink-Verheij JCIY, Otten JDM, et al. Mammography screening and risk of breast cancer death: A population-based case-control study. Cancer Epidemiol Biomarkers Prev 2011, December 6 [Epub ahead of print] doi: 10.1158/1055-9965).

2. Aarts MJ, Voogd AC, Duijm LEM, Coebergh JWW, Louwman WJ. Socioeconomic inequalities in attending the mass screening for breast cancer in the south of the Netherlands—associations with stage at diagnosis and survival. Breast Cancer Res Treat 2011; 128:517–25.

3. Mook S, Van ’t Veer LJ, Rutgers EJ, Ravdin PM, van de Velde AO, van Leeuwen FE, Visser O, Schmidt MK. Independent Prognostic Value of Screen Detection in Invasive Breast Cancer. J Natl Cancer Inst 2011; 103:1– 13.

4. Duffy SW, Cuzick J, Tabar L, Vitak B, Hsiu-His Chen T, Yen MF, Smith RA. Correcting for non-compliance bias in case-control studies to evaluate cancer screening programmes. Appl Statist 2002; 51(Part 2): 235–43.

5. Autier P, Boniol M, LaVecchia C, Vatten L, Gavin A, Héry C, Heanue M. Disparities in breast cancer mortality trends between thirty European

countries: retrospective trend analysis of WHO mortality database. BMJ 2010; 341:c3620.

Mammography screening and breast cancer mortality--Letter

Philippe Autier and Mathieu Boniol

Cancer Epidemiol Biomarkers Prev Published OnlineFirst March 8, 2012.

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