Harding, et al in their article
published in JAMA Intern Med report on associations between
screening mammography and the incidence and mortality from breast cancer, as
well as tumor size.
A study of 16 million women 40
years or older who resided in 547 US counties reporting to the Surveillance,
Epidemiology, and End Results cancer registries during the year 2000. Of these
women, 53 207 were diagnosed with breast
cancer that year and were followed up for the next 10 years.
Across the US counties, there was a
positive correlation between the extent of screening and breast cancer
incidence but not with breast cancer mortality. An absolute increase of 10
percentage points in the extent of screening was accompanied by 16% more breast
cancer diagnoses but no significant change in breast cancer deaths. In an
analysis stratified by tumor size, they found that more screening was strongly
associated with an increased incidence of small breast cancers (≤2 cm) but not
with a decreased incidence of larger breast cancers (>2 cm). An increase of
10 percentage points in screening was associated with a 25% increase in the incidence
of small breast cancers and a 7% increase in the incidence of larger breast
cancers.
They found that screening mammography
results in the diagnosis of additional small cancers but no concomitant decline
in the detection of larger cancers, which might explain the absence of any
significant difference in the overall rate of death from the disease. Together,
these findings suggest widespread overdiagnosis.
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