Screening for Breast Cancer at Younger Ages Linked to Reduced Mortality

Screening women aged 40 to 49 years for breast cancer each year reduced mortality by 25% in the first 10 years of commencing screening compared with the usual practice of screening every 3 years from ages 50 to 70 years upon invitation from the National Health Service Breast Screening Programme (NHSBSP), which is the common practice in the United Kingdom, report study results in The Lancet Oncology. Initiating earlier screening also did not lead to overdiagnosis.

"This is a very long term follow-up of a study which confirms that screening in women under 50 can save lives,” Professor Stephen Duffy, BSc, lead researcher, said in a statement announcing the results. “The benefit is seen mostly in the first 10 years, but the reduction in mortality persists in the long term at about one life saved per thousand women screened.”

The primary study end point was mortality from breast cancer before first NHSBSP screening, and the overall median (interquartile range [IQR]) follow-up was 22.8 (IQR, 21.8-24.0) years.

At the February 28, 2017, cutoff/final follow-up, deaths in the control group outpaced those in the intervention group by almost 3 to 1: 219 vs 83 (relative risk [RR], 0.75; 95% CI, 0.58-0.97; P = .029), marking a statistically significant 25% reduction in 10-year mortality from the earlier screening intervention. This equates to 11.5 years saved per 1000 earlier-screened women.

Beyond the 10-year mark, however, no significant reduction was seen, at 255 deaths in the control group compared with 126 in the intervention group (RR, 0.98; 95% CI, 0.79-1.22; P = .86).

Total deaths for the entire 23-year follow-up period were 10,439, but 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 vs the intervention group: 8442.5 (95% CI, 7766.2-9118.7) vs 3632.4 (95% CI, 3201,1-4063.6), which are the equivalent of 78.9 and 67.4 life-years lost, respectively, per 1000 women.

This randomized controlled study, the UK Breast Screening Age Trial, was led by Queen Mary University of London researchers who 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 1:2 to the intervention group (early annual screening up to age 48 years; n = 53,883 [33.5%]) or the control group (no screening until age 50; n = 106,953 [66.5%]). Those in the control group were unaware of the study, while those in the intervention group were invited to participate through the mail.

The authors also noted that there was not an increase in overdiagnosed cancers because they would have be caught anyway through NHSBSP screening.

“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,” they concluded. “Reducing the lower age limit for screening from 50 to 40 years could potentially reduce breast cancer mortality.”

Because technology has improved so much from when most of these women were screened in the 1990s, the authors call for additional research into early breast cancer screening-related mortality due to the possibility of it being reduced even further for women aged 40 to 49 years.

Reference

Duffy SW, Vulkan D, Cuckle H, et al. Effect of mammographic screening from age 40 years on breast cancer mortality (UK Age trial): final results of a randomised, controlled trial. Lancet Oncol. Published online August 12, 2020. doi:10.1016/S1470-2045(20)30428-9