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Canadian Journal of Public Health

, Volume 104, Issue 7, pp e437–e442 | Cite as

Measuring the Mortality Impact of Breast Cancer Screening

  • James A. HanleyEmail author
  • Maurice McGregor
  • Zhihui Liu
  • Erin C. Strumpf
  • Nandini Dendukuri
Quantitative Research
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Abstract

Objectives

To i) estimate how large the mortality reductions would be if women were offered screening from age 50 until age 69; ii) to do so using the same trials and participation rates considered by the Canadian Task Force; iii) but to be guided in our analyses by the critical differences between cancer screening and therapeutics, by the time-pattern that characterizes the mortality reductions produced by a limited number of screens, and by the year-by-year mortality data in the appropriate segment of follow-up within each trial; and thereby iv) to avoid the serious underestimates that stem from including inappropriate segments of follow-up, i.e., too soon after study entry and too late after discontinuation of screening.

Methods

We focused on yearly mortality rate ratios in the follow-up years where, based on the screening regimen employed, mortality deficits would be expected. Because the regimens differed from trial to trial, we did not aggregate the yearly data across trials. To avoid statistical extremes arising from the small numbers of yearly deaths in each trial, we calculated rate ratios for 3-year moving windows.

Results

We were able to extract year-specific data from the reports of five of the trials. The data are limited for the most part by the few rounds of screening. Nevertheless, they suggest that screening from age 50 until age 69 would, at each age from 55 to 74, result in breast cancer mortality reductions much larger than the estimate of 21% that the Canadian Task Force report is based on.

Discussion

By ignoring key features of cancer screening, several of the contemporary analyses have seriously underestimated the impact to be expected from such a program of breast cancer screening.

Key words

Cancer screening early diagnosis randomized trials mortality 

Résumé

Objectifs

i) Estimer de combien baisserait la mortalité si l’on proposait aux femmes un dépistage du cancer du sein dès 50 ans et jusqu’à 69 ans; ii) procéder en utilisant les mêmes essais et les mêmes taux de participation que ceux examinés par le Groupe d’étude canadien; iii) mais dans notre analyse, nous guider sur les différences essentielles entre le dépistage et les traitements du cancer, sur l’enchaînement chronologique qui caractérise les baisses de mortalité produites par un nombre limité de dépistages, et sur les données de mortalité annuelles dans le segment de suivi approprié à l’intérieur de chaque essai; et donc iv) éviter les sous-estimations graves qui découlent de l’inclusion de segments de suivi inappropriés, c.-à-d. trop tôt après l’entrée dans l’étude et trop tard après l’abandon du dépistage.

Méthode

Nous nous sommes concentrés sur les ratios annuels des taux de mortalité dans les années de suivi où, d’après le régime de dépistage employé, on pourrait s’attendre à des déficits de mortalité. Comme les régimes diffèrent d’un essai à l’autre, nous n’avons pas groupé les données annuelles de chaque essai. Pour éviter les valeurs statistiques extrêmes dues au petit nombre de décès annuels dans chaque essai, nous avons calculé les ratios des taux selon des fenêtres mobiles de trois ans.

Résultats

Nous avons pu extraire des données annuelles dans les rapports de cinq essais. Les données sont limitées pour la plupart par le petit nombre de cycles de dépistage. Néanmoins, elles donnent à penser que le dépistage de 50 à 69 ans résulterait, à chaque âge entre 55 et 74 ans, en une baisse de la mortalité par cancer du sein beaucoup plus importante que l’estimation de 21% sur laquelle se fonde le rapport du Groupe d’étude canadien.

Analyse

En ne tenant pas compte de certaines caractéristiques clés du dépistage du cancer, plusieurs analyses contemporaines sous-estiment gravement l’impact attendu d’un tel programme de dépistage du cancer du sein.

Mots clés

dépistage du cancer diagnostic précoce essais cliniques randomisés mortalité 

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Copyright information

© The Canadian Public Health Association 2013

Authors and Affiliations

  • James A. Hanley
    • 1
    • 2
    Email author
  • Maurice McGregor
    • 2
  • Zhihui Liu
    • 1
  • Erin C. Strumpf
    • 1
    • 3
  • Nandini Dendukuri
    • 1
    • 2
  1. 1.Department of Epidemiology, Biostatistics and Occupational HealthMcGill UniversityMontrealCanada
  2. 2.Department of MedicineMcGill UniversityMontrealCanada
  3. 3.Department of EconomicsMcGill UniversityMontrealCanada

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