medwireNews: Data from the Netherlands adds to evidence suggesting that that a national breast cancer screening program has minimal impact on reducing breast cancer mortality but leads to considerable overdiagnosis of early-stage breast tumors.
The study, carried out by Philippe Autier (International Prevention Research Institute, Lyon, France) and colleagues found that after 23 years (1989–2012) of the biennial mammography screening program, there was a 5% reduction in breast cancer mortality among Dutch women aged 50 years and older.
However, after accounting for a cohort effect, where mortality declined by approximately 5% between 1995 and 2012 independent of screening, the benefit of screening was effectively reduced to zero.
By contrast, factors other than screening, such as improved breast cancer treatments, led to a 28% reduction in breast cancer mortality during the same period.
The researchers report that the incidence of advanced (stage II–IV) breast cancers in women aged 50 years or older remained more or less stable over time, at 168 cases per 100,000 women in 1989 and 166 per 100,000 in 2012.
Conversely, the incidence of in situ cancers increased around sixfold from a rate of 12 per 100,000 in 1989 to 63 per 100,000 in 2012, and stage I cancers increased threefold from 64 to 176 per 100,000.
During the same period, rates in women aged 50 years or younger or 75 years and older, that is, those who did not receive screening, increased by 2.6-fold for in situ cancers and by 1.3-fold for stage I cancers.
Using these data, Autier and team estimated that 54% of in situ and stage I cancers and 33% of all breast cancers detected by mammography were overdiagnoses, that is, they would never have been detected during a woman’s lifetime in the absence of screening.
Taken together, these findings suggest that for one woman who would not die from breast cancer due to screening, approximately 16 would be overdiagnosed with an in situ or a stage I cancer.
Writing in The BMJ the researchers conclude that the Dutch national mammography screening program has had “little influence on the decreases in breast cancer mortality observed over the past 24 years.”
They add: “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.
“In contrast, the extent of overdiagnosis is continuously increasing with the invitation of older women to screening and the adoption of imaging technologies able to detect increasingly smaller breast tumours, most of which are of unknown clinical importance.”
By Laura Cowen
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