Twenty-four years’ worth of data from the Netherlands’ mammography screening program suggest that it has achieved only a marginal impact on breast cancer mortality, according to a paper published online Dec. 5 in the British Medical Journal.
Researchers used data on the stage-specific incidence of breast cancer in the Netherlands during 1989-2012 and estimated the mortality effect of a nationwide, population-based mammography breast cancer screening program, which was introduced in 1988 and targeted women aged 50-75 years.
While there were considerable increases in the incidence of in situ tumors and stage 1 cancers during 1989-2012, the incidence of stages 2-4 cancers was relatively stable over this period. In women aged more than 50 years, who would have been eligible to participate in the screening program, the incidence of stages 2-4 cancers decreased by a nonsignificant 0.16%; from 168/100,000 women in 1989 to 166/100,000 in 2012.
Even when researchers limited their analysis to the period from 1995 to 2012, when the screening program was fully operational and participation rates were around 80%, the incidence of stages 2-4 cancers remained steady. It was also stable in women younger than 50 years, who would not have been eligible for screening.
To estimate the effects of mammography screening on mortality, researchers assumed a scenario without efficient treatment of breast cancer, in which the mortality increase of 0.09% per year seen from 1967 to 1995 would persist until 2012. Under this scenario, they calculated that screening would have at least prevented the predicted 2% increase in breast cancer mortality over that period. Combined with the 0.16% nonsignificant reduction in stages 2-4 cancers over the 23 years of screening, this equated to a total mortality decrease of around 3%.
This reduction paled in comparison to the contributions made by improved treatment and patient management, which the authors suggested would be associated with a 28% reduction in mortality.
“The data on advanced breast cancer in the Netherlands indicate that the Dutch national mammography screening programme would have had little influence on the decreases in breast cancer mortality observed over the past 24 years,” wrote, and his colleagues from the International Prevention Research Institute in Lyon, France. “This conclusion accords with the mounting evidence that randomised trials have overestimated the ability of mammography screening to reduce the risk of deaths from breast cancer in the entire life period after first exposure to mammography screening.”
However, mammography screening also was associated with a sixfold increase in the incidence of in situ cancers among women aged 50-74 years, over the 23-year study period.
The incidence of stage 1 cancers tripled in woman aged 50-69 years, and increased 3.5-fold in those aged 70-74 years. In comparison, over the same period the rates of stage 1 cancers in women younger than 50 years or older than 75 years increased 1.3-fold.
This amounted to a 50% increase in in situ and stage 1 cancers diagnosed among women who were invited to screening, compared with those younger than 50 years. Even in a best-case scenario, the advent of digital mammography would mean 10,038 overdiagnosed cancers for 640 breast cancer deaths prevented by screening.
“Thus for 1 woman who would not die from breast cancer because of screening, about 16 women would be overdiagnosed with an in situ or a stage 1 cancer,” the authors wrote. “Hence, the advent of digital technologies has probably worsened the overdiagnosis problem without clear evidence for improvements in the ability of screening to curb the risk of breast cancer death.”
The study was partly supported by the International Prevention Research Institute. No conflicts of interest were declared.
SOURCE: Autier P et al. BMJ. 2017 Dec 5;359:j5224.