ABSTRACT: In this article, we
discuss the most common epidemiological methods used for evaluating the ability
of mammography screening to decrease the risk of breast cancer death in general
populations (effectiveness). Case-control studies usually find substantial
effectiveness. However when breast cancer mortality decreases for reasons
unrelated to screening, the case-control design may attribute to screening
mortality reductions due to other causes. Studies based on incidence-based
mortality have obtained contrasted results compatible with modest to
considerable effectiveness, probably because of differences in study design and
statistical analysis. In areas where screening has been widespread for a long
time, the incidence of advanced breast cancer should be decreasing, which in
turn would translate into reduced mortality. However, no or modest declines in
the incidence of advanced breast cancer has been observed in these areas.
Breast cancer mortality should decrease more rapidly in areas with early
introduction of screening than in areas with late introduction of screening.
Nonetheless, no difference in breast mortality trends has been observed between
areas with early or late screening start. When effectiveness is assessed using
incidence-based mortality studies, or the monitoring of advanced cancer
incidence, or trends in mortality, the ecological bias is an inherent
limitation that is not easy to control. Minimization of this bias requires data
over long periods of time, careful selection of populations being compared and
availability of data on major confounding factors. If case-control studies seem
apparently more adequate for evaluating screening effectiveness, this design
has its own limitations and results must be viewed with caution.
Source: Breast cancer screening:
evidence of benefit depends on the method used. Autier P (Philippe.autier@i-pri.org),
Boniol M (mathieu.boniol@i-pri.org).
BMC
Med. 2012 Dec 12;10(1):163.
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