US panel finds insufficient evidence to support mammography
BMJ 2002; 324 doi: https://doi.org/10.1136/bmj.324.7332.255 (Published 02 February 2002) Cite this as: BMJ 2002;324:255
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When translated to population level, small benefits from preventive
measures, such as breast cancer screening and cholesterol lowering, may
seem exciting. For the individual it may be more relevant to know the
chance of surviving with and without prevention. To illustrate, I
extracted the 6-7 years breast cancer mortality for screened and non-
screened women from the mammography trial with the most favourable outcome
(1)(first column). I compared these figures with the 6.5 year total
mortality (calculated from annual mortality) for life-long non-smokers and
heavy smokers according to the British Physicians follow-up study
(2)(second column).
Relative risk reduction -45 % -57.7 % Absolute risk reduction -0.13 % -15 % Alive without “intervention” 99.72 % 80.4 % Alive with “intervention” 99.85 % 91.5 %
The table shows the fallaciously positive impression given by
calculating the relative risk reduction. Thus, the benefit from being a
life-long non-smoker, calculated that way, was only a little better than
the benefit from being screened for breast cancer (57.7 % versus 45 %),
although the absolute risk reduction was 115 times greater. How many women
may be interested in regular mammography given that the chance not to die
from breast cancer the next 6-7 years may increase from 99.72 % to 99.85
%, at best?
The figures are not directly comparable due to differences in age,
and length of prevention. The benefit from mammography may increase by
time, but so will the burden of adverse effects. Whereas non-smoking has
no negative consequences for health, the many false-positive mammographic
findings may give rise to much unnecessary and harmful therapy (3). Note
also that the table gives the most optimistic mammography figures. Benefit
from breast cancer screening was seen only in some of the trials and only
as regards breast cancer mortality, not total mortality(4).
1. Bjurstam N, Björneld L, Duffy SW et al. The Gothenburg breast
screening trial: First results on mortality, incidence, and mode of
detection for women ages 39-49 years at randomisation. Cancer 1997; 80:
2091-9.
2. R Doll, R Peto, K Wheatley, R Gray, I Sutherland. Mortality in relation
to smoking: 40 years' observations on male British doctors. BMJ 1994; 309:
901-11.
3. Olsen O, Gøtzsche PC. Cochrane review on screening for breast cancer
with mammography. Lancet. 2001;358:1284-5.
4. Gøtzsche PC, Olsen O. Is screening for breast cancer with mammography
justifiable? Lancet 2000;355:129-34
Competing interests: Relative risk reduction -45 % -57.7 %Absolute risk reduction -0.13 % -15 %Alive without “intervention” 99.72 % 80.4 %Alive with “intervention” 99.85 % 91.5 %
From a common sense view, the goal and value of screening mammography
should not be judged effective or not by the reduction in breast cancer
death rates. It is a detection tool, which when followed by diagnostic
mammography, aims to diagnose non-palable breast cancers before a woman,
or her physician, could otherwise become aware of malignant change.
Screening mammagraphy does this, though not perfectly so.
Cancer mortality rates are a reflection of treatment modalities.
Breast cancer therapy has undergone significant modification over the last
few years and it is premature to assess what these changes will effect on
mortality rates.
Early detection and curative treatment should remain the goal.
Currently, there is no other screening technique that is as effective as
mammagraphy in detecting non-palpable early malignant change. Screening
mammography should, of course, continue to be promoted.
Competing interests: No competing interests
My first impression is that epidemiologists are making too much
confusion.
We cannot say that mammography is unuseful (because this is the only
message that arrive to women), solely on the basis of a review regarding
studies conducted 15 or 30 years ago.
Mammography is greatly improved from that years, new techniques are
coming; ultrasound, techniques of biopsis, surgery and the whole knowledge
of the disease are improved.
Old studies could be criticized or not, this does not mean that, in 2002,
the whole diagnosis (and consequently therapy), of breast cancer is
unuseful (again, this is the potential message).
Don't forget that such an article will appear, soon or late, on newspapers
and women'journals, without an adequate comment. We must be very careful!!
Competing interests: No competing interests
Your news item on mammography screening gives a false impression of
the NCI press release. It implies that the NCI no longer support
screening whereas they state
(http://newscenter.cancer.gov/pressreleases/mammstatement31jan02.hmtl)
that
they continue to recommend women in their forties should be screened every
one to two years with mammography,
women aged 50 and older should be screened every one to two years
and women who are at higher than average risk of breast cancer should seek
expert medical advice. Whilst many might agree with the sentiment of your
item you should not let your prejudices cloud the reporting of others
press releases.
Competing interests: No competing interests
We will be watching what the NCI does very closely and with great
interest. We have not yet seen the redrafted statement for the NCI's
website, so feel we cannot make comment until we know exactly what changes
have been made.
We are also working with independent experts to fully review the
evidence raised by Gotzsche and Olsen. The International Agency for
Research on Cancer (IARC) is producing a comprehensive research paper on
screening for breast cancer, the results of which should be available in
March 2002.
It would be very worrying if women's confidence in screening were to
be undermined based on this re-assessment of trials that took place over
15 years ago, and even then showed positive benefit to women with breast
cancer.
Julietta Patnick, National Coordinator, NHS Cancer Screening
Programmes
Competing interests: No competing interests
Response from the NHS Cancer Screening Programmes, Friday 1 February
The NHS Breast Screening Programme today (FRI Feb 1) said women
should not be alarmed at a repeated debate about the value of early breast
screening trials.
The British Medical Journal and The Lancet are reporting on a
decision by an expert panel for the USA's National Cancer Institute - the
Physicians Data Query (PDQ) - to recommend that criticisms of the design
of early Swedish trials are included on the NCI website.
The recommendation has been prompted by a review published last year
in The Lancet. The authors of the review, Ole Olsen and Peter Gøtzsche,
said that two of the early Swedish screening trials were not well designed
and there was no evidence to support the effectiveness of mammography.
This prompted great debate, with many British screening experts
questioning the value of the Gøtzsche and Olsen exercise.
The NHS Breast Screening Programme would like to respond with two
points.
Firstly, the NCI has not committed to changing its website. The NCI
has told the NHS Breast Screening Programme: "There has been nothing
posted on our website because the NCI guideline has not changed due to the
PDQ meeting. As you probably know, the PDQ is sponsored by the NCI but
not part of the NCI. They are an expert panel. When they come out with a
recommendation, possibly in April, the NCI will take it under advisement.
Our guideline will not necessarily change in response to whatever the
panel recommends."
Furthermore, the NCI's Director of Cancer Prevention, Dr Peter
Greenwald, has recently gone on the record in support of mammograms in
response to this story: "NCI believes early detection is one of the most
important approaches to cancer control. NCI recommends mammography for
women starting in their 40s." (Reuters, 24.1.02).
Secondly, the NHS Breast Screening Programme is working with
independent experts to review fully the evidence raised by Gøtzsche and
Olsen. The International Agency for Research on Cancer (IARC) is
producing a comprehensive review on screening for breast cancer, the
results of which should be available in March 2002.
The NHS Breast Screening Programme would also like to draw attention
to a new perspective on the screening debate detailed by Claudia Henschke
and colleagues from Cornell Medical Center, New York, USA. They reviewed
the Swedish trial previously reviewed by Gøtzsche and Olsen and concluded
that reduction in breast cancer mortality is apparent after sufficient
time has elapsed - around seven years - for the influence of successful
screening and treatment to take effect. They state that the reduction in
breast cancer mortality is substantial (55%) for women aged 55 years or
older at entry to the study who were followed up 8-11 years after
screening. (The Lancet 3.2.02).
Julietta Patnick, National Coordinator, NHS Breast Screening
Programme, comments:
“At this point, we very much hope this academic debate will not
undermine the life-saving work carried out every day across the UK in
looking for, and finding, early breast cancers.”
"It is right and proper that criticism of the screening system should
be fully available in the public domain, such as on the NCI website, in
the British Medical Journal, Lancet, or anywhere else. The benefits as
well as the risks needed to be considered. We are very encouraged by the
findings of Cornell Medical Center, and believe we should be contributing
our own positive evidence by the end of this decade.
Mrs Patnick added: "We will be watching what the NCI does very
closely and with great interest. Until we see whether there is a
redrafted statement on the NCI's website, we cannot make an informed
comment.
"It would be very worrying if women's confidence in screening were to
be undermined based on this re-assessment of trials that took place over
15 years ago, and even then showed positive benefit to women with breast
cancer."
Statistics for NHS Breast Screening Programme 1999/2000:
The programme has detected more cancers than ever before, 9,525 (6.39 per
1000) an increase of 8.6 per cent on 98/99.
4,041 invasive cancers smaller than 15mm were detected - an increase
of 8.6 per cent on 1997/98. Cancers smaller than 15mm are usually
impossible to feel with the human hand, therefore screening has found
these cancers before they would normally be identified. Detecting these
cancers through screening means that they will be treated earlier giving
women a greater chance of survival.
The vast majority of breast cancers (over 60 per cent) are diagnosed
in women attending for a subsequent screen thus emphasising the importance
of women accepting invitations for repeat screening.
The number of women invited for screening (1,811,541) rose again this
year in line with the expected increase in the numbers of women in the
target age group. Acceptance (1,365,636) was steady amongst all women
invited, as was the number of women recalled for assessment.
Competing interests: No competing interests