Anthony B. Miller, MD, from the University of Toronto, and colleagues conducted follow-up analyses of a randomized screening trial involving 89,835 women aged 40–59 years. The women were assigned to mammography (five annual mammography screens; 44,925 women) or control (no mammography; 44,910 women) from 1980–1985. Participants were followed for up to 25 years.
The researchers found that, during the screening period, 666 invasive breast cancers were diagnosed in the mammography arm and 524 were diagnosed in the control arm. And, 180 and 171 of these women, respectively, died of breast cancer during follow-up (hazard ratio for death from breast cancer diagnosed during the screening period associated with mammography, 1.05; 95% confidence interval [CI], 0.85–1.30). During the entire study period, 3,250 women in the mammography arm and 3,133 in the control arm had a diagnosis of breast cancer, and 500 and 505, respectively, died of breast cancer. Cumulative mortality from breast cancer was similar between the two groups (hazard ratio, 0.99; 95% CI, 0.88–1.12). In the mammography arm, there was a residual excess of 106 cancers after 15 years of follow-up, due to over-diagnosis.
“The data suggest that the value of mammography screening should be reassessed,” the authors write.