New data will add fuel to the ongoing debate over the age at which mammography screening for breast cancer should begin. Many guidelines recommend starting at age 50.
But yearly mammography between the ages of 40 and 49 years was associated with a “substantial and significant” 25% reduction in breast cancer mortality during the first 10 years of follow-up, according to new data from the UK Age Trial.
The researchers calculated that 1,150 women needed to undergo screening in the age group of 40-49 years to prevent 1 breast cancer death, or about 1 breast cancer death prevented per 1,000 screened.
However, they also noted that, in the years since the trial first began, there have been improvements in the treatment of breast cancer, so “there might be less scope for screening to reduce mortality in our current era.”
The study was published online August 12 in Lancet Oncology.
“Our results do indicate that screening before age 50 does indeed prevent deaths from breast cancer, with a minimal additional burden of overdiagnosis,” said lead author Stephen W. Duffy, MSc, director of the policy research unit in cancer awareness, screening and early diagnosis, at Queen Mary University, London.
That said, Dr. Duffy explained they do not expect policy makers to extend the age range on the basis of these results alone. “For one thing, they will want to consider costs, both human and financial.” “For another, at this time, the services are concentrating on recovering from the hiatus caused by the COVID-19 crisis, and, at this time, it would be impractical to try to expand the eligibility for screening.”
“I would say our results indicate that lowering the age range, although not necessarily to 40 but to some age below 50, will be at least worth considering when the current crisis is over,” he added.
Guideline recommendations differ
Breast cancer screening guidelines have generated debate, much of which has focused on the age at which to begin screening.
The U.S. Preventive Services Task Force and American College of Physicians recommend screening every other year, on average, for women between the ages of 50 and 74 years.
However, other organizations disagree. The American College of Radiology and Society of Breast Imaging both recommend annual mammograms starting at age 40, and continuing “as long as they are in good health.”
In the UK, where the study was conducted, a national breast cancer screening program offers mammography to women aged 50-70 years every 3 years.
Given the uncertainty that continues to exist over the optimal age for average-risk women to begin screening, the UK Age Trial set out to assess if screening should begin at a younger age and if that might lead to overdiagnosis of breast cancer.
Results from the study’s 17-year follow-up, published in 2015, showed a reduction in breast cancer mortality with annual screening, beginning at age 40 years, which was significant in the first 10 years after participants were randomized (Lancet Oncol. 2015;16:1123-32).
In the current study, Dr. Duffy and colleagues report on breast cancer incidence and mortality results in the UK Age trial after 23 years of follow-up.
The cohort included 160,921 women enrolled between Oct. 14, 1990, and Sept. 24, 1997, who were randomized to screening (n = 53,883) or the control group (n = 106,953).
Of those screened during the study period, 7,893 (18.1%) had at least one false-positive result. There were 10,439 deaths, of which 683 (7%) were attributed to breast cancer diagnosed during the study period.
At 10 years of follow-up, death from breast cancer was significantly lower among women in the screening versus control group (83 vs 219 deaths; relative risk, 0.75; P = .029).
However, no significant reduction was observed thereafter, with 126 versus 255 deaths occurring after more than 10 years of follow-up (RR, 0.98; 95% confidence interval, 0.79-1.22; P = .86), the authors note.
“This follow-up indicates that the gain in survival was concentrated in the first 10 years after the women began to be screened,” commented Kevin McConway, PhD, emeritus professor of applied statistics at the Open University, Milton Keynes, England.
“In those first 10 years, out of every 10,000 women invited for screening, on average, about 16 died of breast cancer, while in every 10,000 women in the control group who did not get the screening, on average, 21 died. These numbers indicate that lives were saved,” he said.
“But they also indicate that death from breast cancer was pretty rare in women of that age,” he pointed out.
“Because breast cancer deaths in younger women are not common, the estimates of breast cancer death rates are not very precise, despite the fact that the trial involved 160,000 women,” he said.
“Over the whole follow-up period so far, the difference in numbers of deaths between those who were screened in their 40s and those who were not is 6 deaths for every 10,000 women, but because of the statistical uncertainty, this figure could plausibly be larger, at 13 per 10,000. Or, in fact, the data are also consistent with a very slightly higher death rate [1 death per 10,000 women] in those who had the screening,” Dr. McConway explained.
“But none of those numbers is very large, out of 10,000 women. Allowing for the fact that not every woman invited for screening will actually attend the screening, the researchers estimate that 1,150 women would have to be screened in their 40s to prevent one breast cancer death,” he noted.