25-year study questions value of screening mammography

A new study with up to 25 years’  follow up is reopening debate about the value of screening mammography in women aged 40 to 59. Published in BMJ, the Canadian research found that 22% of women in that screening population-or 1 in every 424-had an over-diagnosed breast cancer.

Nearly 90,000 women aged 40 to 59 from six Canadian provinces were included in the study, which was a follow-up of randomization to either mammographic screening for 5 years or no mammography. Annual breast examinations were performed on all women aged 40 to 49 in the mammography arm and all those aged 50 to 59 in both arms. Women aged 40 to 49 who did not receive mammography underwent a single breast examination followed by usual care in the community.

Among the 44,925 women in the mammography arm, 666 invasive breast cancers were diagnosed during the 5-year screening period, versus 524 in the 44,910 women in the control group. Of those diagnosed, 180 women in the mammography arm and 171 women in the control arm died of breast cancer during the 25-year follow-up period (hazard ratio for mammography 1.05; 95% confidence interval [CI] 0.85 to 1.30).

The cumulative mortality from breast cancer over the entire study period was similar for women who underwent mammography and those who did not (hazard ratio 0.99, 95% CI 0.88 to 1.12). Breast cancer was diagnosed in 3,250 in the mammography arm and 3,133 in the control arm, and 500 and 505 deaths due to the disease were recorded in the two groups, respectively.

The researchers concluded that annual mammography does not reduce breast cancer-related mortality in women aged 40 to 59 beyond that associated with physical examination or usual care, assuming that adjuvant therapy for the disease is readily available. “The data suggest,” the authors said, “that the value of mammography screening should be reassessed.” They cautioned that their data “may not be generalizable to all countries” but noted that for technically advanced countries, their results “support the views of some commentators that the rationale for screening by mammography should be urgently reassessed by policy makers.”

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