Sidney University. Australia: Women who understand the risk of over-detection and over-diagnosis
associated with mammography screening have lower intentions to have a
breast screening test, according to a new Lancet study. "Mammography
screening can reduce breast cancer deaths but most women are unaware
that inconsequential disease can also be detected by screening, leading
to over-diagnosis and overtreatment," says study author, Prof Kirsten McCaffery of the University of Sydney.
Over-detection
and over-diagnosis refers to the diagnosis and treatment of breast
cancer that would not have presented clinically during a woman's
lifetime.
Such a diagnosis, and the resulting overtreatment, can harm women physically and emotionally.
Professor
McCaffery says the first of its kind study "underlines the ethical
imperative for women to have clear decision support materials so that
they can make more informed decisions about whether they want to have a
breast screening mammogram."
"A health system centred around the
individual should assist decision-making that incorporates a woman's
values and preferences, irrespective of whether her eventual choice is
to screen or not.
"Therefore, momentum is shifting from
uninformative and persuasive approaches to screening communication to
clear and balanced information, giving people the opportunity to make
informed choices based on their assessment of the trade-offs between
potential outcomes."
Study and key results:
The study is the
first research to assess the effect of including over-detection
information in decision support materials on choices of women on the
threshold of becoming candidates for mammography screening - women aged
48-50 years.
The women who participated in the study had not had
mammography in the past two years and did not have a personal or strong
family history of breast cancer.
The randomised control trial of
879 women found that compared to controls, in women provided with
decision support containing explanatory and quantitative information
about over-detection:
- significantly more women had adequate
knowledge about breast cancer screening and made an informed choice
whether to be screened
- there were significantly less favourable
attitudes towards breast cancer screening, although attitudes remained
positive overall
- significantly fewer women intended to be screened for breast cancer.
Decision support materials
The
intervention decision aid contained evidence-based information about
important outcomes of breast screening over 20 years, compared with no
screening — that is, breast cancer mortality reduction, over-detection,
and false positives. The control version omitted all content about
over-detection but was otherwise identical to the intervention decision
aid.
Quantitative evidence included in the decision aids was taken
from an updated version of a published model of mammography screening
outcomes for women in Australia.
The model incorporates estimates
of both over-detection and the reduction in breast cancer mortality from
screening, which were derived from a meta-analysis of randomised trial
data and adjusted to account for the effect of regularly undergoing
screening.
These estimates were applied to current Australian data
for incidence and mortality to quantify cumulative outcomes of biennial
screening from age 50-69 years versus no screening over this period.
This
information was presented in a short booklet for women, combining text
and visual formats. The expected frequencies of outcomes were
illustrated with icon arrays depicting the absolute numbers affected per
1000 women screened over 20 years from age 50 years.
Media enquiries: Dan Gaffney, 048 100 4782, daniel.gaffney@sydney.edu.au