Impact of screening mammography on mortality from breast cancer before age 60 in women 40 to 49 years of age

  • S. Narod Dalla Lana School of Public Health
  • P. Sun Women’s College Research Institute, Women’s College Hospital
  • C. Wall Dalla Lana School of Public Health
  • C. Baines Dalla Lana School of Public Health
  • A.B. Miller Dalla Lana School of Public Health
Keywords: breast cancer, screening, mammography, mortality

Abstract

Background

Whether screening mammography programs should include women in their 40s is controversial. In Canada, screening of women aged 40–49 years has not been shown to reduce mortality from breast cancer. Given that screening mammography reduces mean tumour size and that tumour size is inversely associated with survival, the lack of benefit seen with screening is puzzling and suggests a possible adverse effect on mortality of mammography or subsequent treatment (or both) that counterbalances the expected benefit derived from downstaging.

Methods

We followed 50,436 women 40–49 years of age until age 60 for mortality from breast cancer. Of those women, one half had been randomly assigned to annual mammography and one half to no mammography. The impact of mammography on breast cancer mortality was estimated using a left-censored Cox proportional hazards model.

Results

Of 256 deaths from breast cancer recorded in the study cohort, 134 occurred in women allocated to mammography, and 122 occurred in those receiving usual care and not allocated to mammography. The cumulative risk of death from breast cancer to age 60 was 0.53% for women assigned to mammography and 0.48% for women not so assigned. The hazard ratio for breast cancer–specific death associated with 1 or more screening mammograms before age 50 was 1.10 (95% confidence interval: 0.86 to 1.40).

Conclusions

Mammography in women 40–49 years of age is associated with a small but nonsignificant increase in the risk of dying of breast cancer before age 60. Caution should be exercised when recommending mammographic screening to women before age 50.


Published
2014-07-03
How to Cite
Narod, S., Sun, P., Wall, C., Baines, C., & Miller, A. (2014). Impact of screening mammography on mortality from breast cancer before age 60 in women 40 to 49 years of age. Current Oncology, 21(5), 217-221. https://doi.org/10.3747/co.21.2067
Section
Clinical Trials