Yearly mammography beginning at age 40 years may reduce breast cancer mortality
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Annual mammography beginning at age 40 or 41 years led to a reduction in breast cancer mortality while adding little to the burden of overdiagnosis, according to results of a randomized study in the U.K. published in The Lancet Oncology.
Reducing the lower age limit for screening to 40 years could reduce overall breast cancer mortality, researchers noted.
“This is a very long-term follow-up of a study which confirms that screening in women [aged younger than 50 years] can save lives,” Stephen Duffy, MSc, director of the policy research unit in cancer awareness, screening and early diagnosis at Queen Mary University of London, said in a press release. “The benefit is seen mostly in the first 10 years, but the reduction in mortality persists in the long term at about one life saved per thousand women screened.”
The appropriate age at which to start breast screening remains uncertain.
A breast cancer screening program in the U.K. offers mammography every 3 years to women aged 50 to 70 years. In the U.S., American Cancer Society recommends women be given the choice to start annual mammograms at age 40 years and that all women begin receiving yearly mammograms at age 45 years with the option to switch to every 2 years starting at age 55 years.
Duffy and colleagues randomly assigned women aged 39 to 41 years — stratified by general practice — to yearly mammographic screening from the year of trial inclusion up to and including the year they turned age 48 years (intervention group, n = 53,883) or to standard care of no screening until invitation to National Health Service breast screenings starting at age 50 years (control group, n = 106,953).
Researchers recruited women for the intervention group via postal invitation. Women in the control group were not aware of the study.
Mortality from breast cancer diagnosed during the intervention period — between 1990 and 1997 — prior to first National Health Service screening served as the study’s primary endpoint.
Median follow-up was 22.8 years (interquartile range, 21.8-24).
Results showed a significant reduction in breast cancer mortality at 10 years of follow-up, with 83 deaths of breast cancer in the intervention group compared with 219 deaths in the control group (RR = 0.75; 95% CI, 0.58-0.97).
Researchers observed no significant reduction after that, with 126 deaths in the intervention group and 255 deaths in the control group after more than 10 years of follow-up (RR = 0.98; 95% CI, 0.79-1.22). They calculated 11.5 (95% CI, 1-22) years of life saved per 1,000 women invited to earlier screening, for a total of 620 years of life saved. Overdiagnosis appeared modest at worst in the younger age group and minimal beyond what would occur when screening women aged 50 years and older, according to the researchers.
“We now screen more thoroughly and with better equipment than in the 1990s, when most of the screening in this trial took place, so the benefits may be greater than we’ve seen in this study,” Duffy said in a press release.
The debate over when to begin breast screening will not be settled by this study, Anthony B. Miller, MD, professor emeritus at Dalla Lana School of Public Health at University of Toronto, wrote in an accompanying editorial.
“Although Duffy and colleagues should be commended for providing long-term data from a well-conducted study, it could be argued that breast screening with mammography should not be initiated at any age, but rather women should be encouraged to practice breast awareness, with mammography used as a diagnostic test, while always remembering that in young women, mammography can be negative even in the presence of physically detectable breast cancer,” Miller wrote. “This approach is akin to the WHO recommendations on cancer early diagnosis.”
References
- American Cancer Society. American Cancer Society Breast Cancer Screening Guideline. Available at: www.cancer.org/latest-news/special-coverage/american-cancer-society-breast-cancer-screening-guidelines.html. Accessed Aug. 13, 2020.
- Duffy SW, et al. Lancet Oncol. 2020;doi:10.1016/S1470-2045(20)30398-3.
- Miller AB. Lancet Oncol. 2020;doi:10.1016/S1470-2045(20)30428-9.
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