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may be reasonable to attend for breast
cancer screening with mammography, but it may
also be reasonable not to attend because screening has both
benefits and harms
2000 women are screened regularly for 10 years,
one will benefit from the screening,
as she will avoid dying from
the same time, 10 healthy women will, as a consequence,
become cancer patients and will be treated unnecessarily.
These women will have either a part of their breast
or the whole breast removed, and they will often receive
radiotherapy and sometimes chemotherapy
about 200 healthy women will experience a false
alarm. The psychological strain until one knows
whether it was cancer, and even afterwards, can
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27 January 2009, doi:10.1136/bmj.b86
Cite this as: BMJ 2009;338:b86
screening: the facts—or maybe not
Peter C Gøtzsche, director1,
Ole J Hartling, consultant2,
Margrethe Nielsen, PhD student1,
John Brodersen, lecturer3,
Karsten Juhl Jørgensen, researcher1
Nordic Cochrane Centre, Rigshospitalet, Blegdamsvej 9, DK-2100
Copenhagen, Denmark, 2 Department of Nuclear
Medicine, Vejle Sygehus, Denmark, 3 Department
of General Practice, University of Copenhagen, Denmark
Gøtzsche and colleagues argue that women are still
not given enough, nor correct, information about the
harms of screening
years ago, we published a survey of the information given
to women invited for breast screening with mammography
in six countries with publicly funded screening
The major harm of screening, which is overdiagnosis
and subsequent overtreatment of healthy women,
was not mentioned in any of 31 invitations.1
Ten invitations argued that screening either leads
to less invasive surgery or simpler treatment,
although it actually results in 30% more surgery,
20% more mastectomies, and more use of radiotherapy2
because of overdiagnosis.3
4 Pain caused by the procedure was mentioned
in 15 invitations, although it is probably the least
serious harm, as it is transient.
then, little has changed. Our 2006 article included a
box with recommended information and numbers needed
to benefit and to harm.1
Although the information leaflet used in the United
Kingdom has since been updated,5
the contents remain essentially the same. The
leaflet has the authoritative title Breast Screening:
suggesting that the information can be trusted. Here,
we discuss why it is inadequate as a basis for informed
consent and introduce our leaflet, which we think
provides the information on the benefits and
harms of breast screening that women need to
make a rational decision.
revised leaflet emphasises the benefits of screening. The
first page leaves no doubt that screening is good
for women, with its second heading: "Why
do I need breast screening?" Furthermore, it
states, "If changes are found at an early stage, there
is a good chance of a successful recovery, "
and "Around half the cancers that are found
at screening are still small ... This means that
the whole breast does not have to be removed." It
also tells women that screening saves "an estimated
1400 lives each year in this country" and
"reduces the risk of the women who attend
dying from breast cancer."
contrast, little information is given about harms. It states
that "some women" find mammography uncomfortable
or painful, which becomes "many women"
in the summary. The summary also notes that
recalls for more investigations "can cause worry."
No mention is made of the major harm of screening—that
is, unnecessary treatment of harmless lesions that
would not have been identified without screening.
This harm is well known and acknowledged, even
among screening enthusiasts.3
It is in violation of guidelines and laws for
informed consent not to mention this common harm,
especially when screening is aimed at healthy
7 The new guidelines from the General Medical
Council state: "You must tell patients if an investigation
or treatment might result in a serious adverse outcome,
even if the likelihood is very small."6
The likelihood of being overdiagnosed after mammography
is not very small; it is ten times larger than
the likehood of avoiding death from breast cancer.1
harm is false positive diagnoses. The leaflet notes
that about one in every 20 women screened will be
recalled for more tests, but does not explain
that this 5% rate applies to only one round
of screening. The rate of false positive diagnosis
after 10 screenings was 50% in the United States and
20% in Norway.8
9 We now know that the psychosocial strain of
a false alarm can be severe and may continue
after women are declared free from cancer.10
Many women experience anxiety, worry, despondency,
sleeping problems, and negative impact on sexuality
and behaviour, and changes in their relationships
with family, friends, and acquaintances and in
11 This can go on for months, and some
women will feel more vulnerable about disease and
will see a doctor more often.12
third harm is caused by radiotherapy of overdiagnosed women.
The leaflet states that a mammogram "involves
a tiny dose of radiation, so the risk to your
health is very small." The rate of overdiagnosis
was 30% in randomised trials of screening and 50%
in observational studies.2
14 We therefore believe it is misleading
to assure women that the radiation dose from the mammogram
is tiny, without telling them that the much bigger
dose used in radiotherapy is harmful when given to
healthy people. Comparison of left sided with
right sided irradiation suggests that radiotherapy
may double the mortality from heart disease and
Technological improvements may have diminished these
harms to some extent, but they are still important.
summary implies that screening leads to fewer mastectomies.
This is incorrect. Screening led to 20% more mastectomies
in randomised trials4
and observational studies have confirmed that
the number of mastectomies increases when screening is
These initial increases are not compensated for by
reduced rates among older women who are no longer screened
(unpublished national data, Danish National Board
in situ is not mentioned in the leaflet, although it
constitutes about 20% of the diagnoses made at screening
in the UK. Fewer than half of the cases progress to
invasive cancer, and 30% are treated with mastectomy.16
A patient representative has described her experience
of gaining this information as trying to "uncover
a closely guarded state secret."4
are no reservations in the leaflet about screening older
women, only a scare that the breast cancer risk increases
with age, although it has not been shown that
screening these women decreases their risk of
dying from breast cancer. Furthermore, the problem
with overdiagnosis becomes more pronounced, and the
likehood of gaining any benefit smaller, due to competing
risks of death.
it has not been proved that screening saves lives.
There is an inevitable bias in assessment of cause
of death that can be particularly difficult when
women have more than one cancer.2
Trials show that breast screening does not decrease
total cancer mortality. The relative risk was 1.02
(95% confidence interval 0.95 to 1.10) in the
two most reliable trials and 0.99 in the others,
and there is no reliable evidence that screening decreases
although half a million women participated in
the screening trials. This indicates that the benefit of
screening is likely to be smaller than generally
have written an evidence based leaflet (see bmj.com) to
help women decide about breast screening. As
it describes benefits and harms in numbers that
can readily be understood and uses the same denominator
throughout: 2000 women screened every two years
for 10 years.
tested draft versions among general practitioners in Denmark,
Norway, and Sweden belonging to the Nordic Risk Group
Network and among lay people, which led to considerable
improvements. A physician noted that it was unbalanced
because we had listed several harms but only
one benefit. We therefore tried to list more
benefits, but realised that there is only one important
benefit, the reduction in breast cancer mortality.
It is often claimed that a normal mammography
result reassures women that they are healthy.
But most women will feel healthy before they are
invited to screening, and the invitation may also cause
insecurity as well as false security because about
half of the breast cancers that require treatment
are found between screening rounds.3
Therefore, screening creates security, insecurity,
and false reassurance.
box gives the summary from the leaflet. We hope it provides
sufficient information to enable women, together
with their family and general practitioner, to
decide whether to participate.4
The leaflet was distributed to general practitioners
and gynaecologists in Denmark in March 2008.
It is available in English and Danish and can
be downloaded from bmj.com, screening.dk, or cochrane.dk.
It will be translated into Icelandic, Norwegian, Swedish
and Finnish and we aim to update it when necessary.
Summary from evidence based leaflet
It may be reasonable to attend
for breast cancer screening with mammography,
but it may also be reasonable
not to attend because screening has both
benefits and harms
If 2000 women are screened regularly for
10 years, one will benefit from the
screening, as she will avoid dying
from breast cancer
At the same time, 10 healthy women
will, as a consequence, become cancer
patients and will be treated
unnecessarily. These women will have either
a part of their breast or the
whole breast removed, and they will often
receive radiotherapy and sometimes
Furthermore, about 200 healthy
women will experience a false alarm. The
psychological strain until one
knows whether it was cancer, and even afterwards,
can be severe
one sided propaganda about breast screening is a global
phenomenon that has resulted in misconceptions about
A survey of American and European women17
found that 68% believed screening reduced their
risk of contracting breast cancer, 62% that screening
at least halved mortality, and 75% that 10 years of
screening saved 10 of 1000 participants (an overestimate
of 20 times2).
Another study showed that only 8% were aware that
participation can harm healthy women18
and that 15% believed their lifetime risk of
contracting the disease was more than 50% (an
overestimate of five times).
UK National Screening Committee agreed in 2000 that the
purpose of information was not to recruit women but
to allow them to choose whether to participate,4
but this decision has not had any effect on the
New evidence that shows less benefit and substantially
more harm from screening than previously thought
has largely been ignored.1
5 We believe that if policy makers
had had the knowledge we now have when they decided
to introduce screening about 20 years ago, when nobody
had published data on overdiagnosis or on the imbalance
between numbers of prevented deaths from breast cancer
and numbers of false positive screening results
and the psychosocial consequences of the false
alarms, we probably would not have had mammography
taking tests continue to experience morbidity and regret
because they found out many of the harms of screening
It may be too late to start asking questions on arrival
to the screening unit, as the UK leaflet suggests.5
There is also a conflict of interest when those
who provide the information are responsible for
the success of the screening programme.1
High participation rates are pivotal, and information
about harms may deter women from participation.
question of whether the benefits of screening outweigh the
harms is a value judgment that needs to be made by
To allow this to happen, the responsibility for the
screening programmes must be separated from the
responsibility for the information material,1
and information materials should be carefully tested
among general practitioners and lay people.
this as: BMJ 2009;338:b86
We thank Hazel Thornton and Michael Baum for comments
on the manuscript.
Contributors and sources: PCG wrote the first draft,
all authors commented on it and are guarantors.
We have all contributed to research on screening,
and four of us wrote an information leaflet about
Funding: Production and distribution of our leaflet
in Denmark was funded by KræftFonden.
Competing interests: None declared.
Provenance and peer review: Not commissioned; externally
KJ, Gøtzsche PC. Content of invitations to publicly
funded screening mammography. BMJ 2006;332:538-41.
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A, Gray M. Screening: evidence and practice. Oxford:
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Medical Council. Consent: patients and doctors making
decisions together. London: GMC, 2008.
N, Broeders M, de Wolf C, Törnberg S, Holland R, von
Karsa L, eds. European guidelines for quality assurance
in breast cancer screening and diagnosis. 4th ed. Luxembourg:
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SW. Ten-year risk of false positive screening mammograms
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KJ, Gøtzsche PC. Overdiagnosis in publicly organised
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