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Mammography did not reduce breast cancer mortality
Women aged 40 to 59 years who underwent annual mammograms experienced similar breast cancer mortality as those who underwent physical examination or usual care, according to 25-year follow-up of a randomized study conducted in Canada.
In addition, researchers found that more than one of every five breast cancers detected during mammography was overdiagnosed, meaning they would not have caused symptoms or posed a threat during the patients’ lifetimes.
“In technically advanced countries, our results support the views of some commentators that the rationale for screening by mammography should be urgently reassessed by policy makers,” Anthony B. Miller, MD, FRCP, FRCP(C), FHPHM, FACE, professor emeritus at Dalla Lana School of Public Health at the University of Toronto, and colleagues wrote.
The randomized screening trial included 89,835 women aged 40 to 59. Miller and colleagues randomly assigned 44,925 women to undergo one mammogram per year for 5 years at one of 15 screening centers in Canada. The women underwent mammograms between 1980 and 1985. The 44,910 women assigned to the control arm did not undergo screening.
Breast-cancer mortality served as the primary outcome measure.
Women in the mammography arm aged 40 to 49 years, as well as all study participants aged 50 to 59 years, underwent annual physical breast examinations. Women in the control arm aged 40 to 49 years underwent a single physical breast examination, followed by usual care in the community.
During the 5-year screening period, researchers reported 666 cases of invasive breast cancers diagnosed in women assigned mammography and 524 cases diagnosed among women assigned to the control arm. Of those women, 180 assigned to mammography and 171 assigned to the control arm died during the 25-year follow-up period.
The overall HR for death from breast cancer diagnosed during the screening period associated with mammography was 1.05 (95% CI, 0.85-1.30).
During the entire 25-year study period, researchers reported 3,250 women in the mammography arm and 3,133 women in the control arm developed breast cancer. Of them, 500 in the mammography arm and 505 in the control arm died.
Researchers calculated a similar cumulative mortality from breast cancer between women in the mammography arm and the control arm (HR=0.99; 95% CI, 0.88-1.12).
At the conclusion of the screening period, Miller and colleagues reported 666 incidences of overdiagnosis in the mammography arm and 524 in the control arm.
“Fifteen years after enrollment, the excess became constant at 106 cancers,” the researchers wrote. “This excess represents 22% of all screen-detected invasive cancers — that is one overdiagnosed breast cancer for every 424 women who received mammography screening in the trial.”
Hans-Olov Adami
In an accompanying editorial, Mette Kalager, MD, Hans-Olov Adami, MD, PhD, and Michael Bretthauer, MD, all from the department of Health Management and Health Economics at the University of Oslo in Oslo, Norway, wrote: “We agree with Miller and colleagues that ‘the rationale for screening by mammography be urgently reassessed by policy makers.’ As time goes by, we do indeed need more efficient mechanisms to reconsider priorities and recommendations for mammography screening and other medical interventions. This is not an easy task, because governments, research funders, scientists, and medical practitioners may have vested interests in continuing activities that are well established.”
For more information:
- Kalager M. BMJ. 2014;doi:10.1136/bmj.g1403.
- Miller AB. BMJ. 2014;doi:10.1136/bmj.g366.
Disclosure: The researchers report no relevant financial disclosures.