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Screening Mammography in Women Younger than 50 Years of Age
- Harold C. Sox, MD
- Dartmouth-Hitchcock Medical Center, Lebanon, NH 03756 Requests for Reprints: Harold C. Sox, MD, Department of Medicine, Dartmouth-Hitchcock Medical Center, One Medical Center Drive, Lebanon, NH 03756.
The current controversy over doing mammography in women younger than 50 years of age illustrates a common problem for the practicing physician: what to do when the evidence is incomplete and the experts cannot agree. The Annals reader can observe this debate in the “In the Balance” section of this issue [1, 2]. Can “evidence-based medicine” provide direction for the practitioner?
Some general principles may help the practitioner decide whether to screen average-risk young women using mammography.
Benefits and Harms of Screening Mammography: A Brief Summary
A meta-analysis of five Swedish randomized trials of screening mammography provides information about the effect of screening mammography on breast cancer mortality [3]. The combined cohort comprised 282 777 women aged 40 to 74 years. The five studies were similar except for the interval between mammograms, which ranged from 18 months to 33 months. The 12-year cumulative mortality from breast cancer was 3.9 deaths per 1000 enrollees in the screened group and 5.1 deaths per 1000 enrollees in the control group. The difference in these two mortality rates is the risk for death from breast cancer that is attributable to not being screened periodically for 12 years (1.2 deaths from breast cancer per 1000 women screened). The inverse of the attributable risk is the number of women aged 40 to 74 years who must be screened for 12 years to prevent one death from breast cancer: 883.
Because of the large size of the combined cohort, the investigators were able to analyze the effect of screening in different age groups. In screened women aged 50 to 59 years, the relative risk for dying of breast cancer was 0.71 (95% CI, 0.57 to 0.89); in screened women aged 60 to 69 years, this risk was also 0.71 (CI, 0.56 to 0.91). Mammographic screening reduced the risk for dying of breast cancer by …
