Annual Mammography May Be Unnecessary, New Study Suggests

The rationale for annual mammography needs to be reassessed, urged the authors of the Canadian National Breast Screening Study.¹

The plea follows the results of the 25-year follow-up study indicating that annual screening in women aged 40 to 59 years did not reduce mortality from breast cancer beyond that of physical examination or usual care. The results of the study, which included over 89,000 women, also showed that 22% of breast cancers detected by mammography were overdiagnosed. That equates to 1 of 424 women who received the screening during the trial, the authors explained. 

Pertinent Points:

- Annual mammography needs to be reassessed, urge the authors of the Canadian National Breast Screening Study.

- Yearly screening of women aged 40-59 years did not reduce mortality from breast cancer beyond that of physical examination or usual care.

“As time goes by we do indeed need more efficient mechanisms to reconsider priorities and recommendations for mammography screening and other medical interventions,” wrote Drs. Mette Kalager, Hans-Olov Adami, and Michael Bretthauer, all of the Department of Health Management and Health Economics, University of Oslo, Norway, and the Department of Epidemiology at Harvard School of Public Health, Boston, in an accompanying editorial.² “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.” 

During the 5-year screening period established in the trial, 666 invasive breast cancers were diagnosed in the mammography arm (n=44,925 participants) and 524 in the control arm (n=44,910), the authors report. Of the positive screenings, 180 women in the mammography arm and 171 women in the control arm died of breast cancer during the 25-year follow-up period. The result was a hazard ratio of 1.05 (95% confidence interval, 0.85 to 1.30).

When delineated by age, the findings were nearly identical for women aged 40 to 49 years and those aged 50 to 59 years, the study authors reported.

Of the 3,250 women who received annual mammography and, subsequently, were given a diagnosis of breast cancer, 500 died. Likewise, of 3,133 women in the control arm who were not screened but who received a diagnosis of breast cancer, 505 died (hazard ratio, 0.99; 95% confidence interval, 0.88 to 1.12).

"Thus, the cumulative mortality from breast cancer was similar between women in the mammography arm and in the control arm," concluded the authors, stressing that the results should not be generalized to all countries but could be applied to technically advanced countries in which adjuvant therapy for breast cancer is readily available.

While the authors note that education, early diagnosis, and excellent clinical care must continue, they emphasized that annual mammography "does not result in a reduction in breast cancer specific mortality for women aged 40-59 beyond that of physical examination alone or usual care in the community."

References:

1. Miller AB, Wall C, Baines CJ, et al. Twenty five year follow-up for breast cancer incidence and mortality of the Canadian National Breast Screening Study: randomised screening trial. BMJ. 2014;348:g366.
2. Kalager M, Adami HO, Bretthauer M. Too much mammography. BMJ. 2014;348:g1403.