Initiating annual breast cancer screening at 40 years of age may reduce mortality rates in women, according to study results published August 12, 2020, in the journal The Lancet Oncology (Duffy SW, et al. Lancet Oncol. 2020;21:1165-1172). Starting earlier screening also did not result in overdiagnosis.
Stephen W. Duffy, MSc, Professor of Cancer Screening, Queen Mary University of London, England, and colleagues conducted a long-term study to determine the effect of mammography on death rates from breast cancer in women aged 40 to 48 years. They recruited 160,921 women aged 39 to 41 years between October 14, 1990, and September 24, 1997, from 23 breast screening units in England, Wales, and Scotland. The women were randomized in a 1:2 ratio to the intervention group (early annual screening up to 48 years of age; N = 53,883 [33.5%]) or the control group (no screening until 50 years of age; N = 106,953 [66.5%]). Those in the control group were unaware of the study, whereas those in the intervention group were invited to participate through the mail. The primary end point of the study was mortality from breast cancer before first National Health Service Breast Screening Programme screening, and the overall median follow-up was 22.8 years.
After 10 years of follow-up, 83 women in the intervention group died of breast cancer compared with 219 women in the control group, which the researchers noted was a significant drop in mortality. After the 10-year mark, the reduction in mortality was not found to be significant, with 126 deaths in the intervention group compared with 255 deaths in the control group.
Total deaths for the entire 23-year follow-up period were 10,439, however only 683 (7%) of these were in the intervention group. In addition, a post-hoc analysis showed almost twice the amount of life-years lost in the control group versus the intervention group: 8442.5 versus 3632.4, which are the equivalent of 78.9 and 67.4 life-years lost, respectively, per 1000 women.
“Yearly mammography before age 50 years, commencing at age 40 or 41 years, was associated with a relative reduction in breast cancer mortality, which was attenuated after 10 years, although the absolute reduction remained constant. Reducing the lower age limit for screening from 50 to 40 years could potentially reduce breast cancer mortality,” the investigators noted.
They also reported that there appeared to be little or no overdiagnosis in cancer beyond that which would occur from screening patients aged 50 years.