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Canadian Journal of Public Health = Revue Canadienne de Santé Publique logoLink to Canadian Journal of Public Health = Revue Canadienne de Santé Publique
. 2013 Nov 1;104(7):e437–e442. doi: 10.17269/cjph.104.4099

Measuring the Mortality Impact of Breast Cancer Screening

James A Hanley 13,23,, Maurice McGregor 23, Zhihui Liu 13, Erin C Strumpf 13,33, Nandini Dendukuri 13,23
PMCID: PMC6973864  PMID: 24495817

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

Footnotes

Acknowledgements: This work was supported by the Canadian Institutes of Health Research.

Conflict of Interest: None to declare.

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