28% were in women aged 70 years or older
(Figure 1),1with little variation by pro vince.
Regular screening for breast cancer with mam-
mography, breast self -examinations and clinical
breast examinations are widely recommended to
reduce mortality due to breast cancer. Although
controversy remains over precisely which
screening services should be provided and to
whom, these methods are frequently used in
Outcomes of screening for breast cancer such
as tumour detection and mortality must be put
into context of the harms and costs of false -
positive results, overdiagnosis and overtreatment.
Consideration of benefits, harms and costs is
complicated by variations in risk factors and in
the types and stages of cancer.
Any positive result from screening has emo-
tional costs such as anxiety and worry for
patients and their families, and financial costs to
both the patient and the health care system as a
result of additional and potentially unnecessary
diagnostic tests. For women with positive results
on screening tests, additional diagnostic tests
will usually be recommended, such as further
mammography, ultrasound and/or tissue sam-
pling with core needle biopsy.
This document updates the previous guidelines
issued by the Canadian Task Force on Preventive
Health Care (2001).5,6The absence of current
Canadian recommendations, the recent contro-
versy over the best way to screen for breast cancer
among women at average risk of the disease,7,8the
availability of new technologies such as magnetic
resonance imaging (MRI) and a recent review of
the evidence9were the basis for selecting this
topic for an update by the revitalized Canadian
Task Force on Preventive Health Care.
Recommendations are presented for the use
of mammography, MRI, breast self-examination
and clinical breast examination to screen for
breast cancer among women at average risk of
f the newly diagnosed cases of breast
cancer in Canada, 80% were in women
over the age of 50 years, and about
disease (defined as those with no previous breast
cancer, no history of breast cancer in a first-
degree relative, no known mutations in the
BRCA1/BRCA2 genes or no previous exposure of
the chest wall to radiation). Re commendations
are provided separately for women aged 40–49,
50–69 and 70–74 years and are aimed at clini-
cians and policy-makers. The recommendations
are intended to inform both organized and oppor-
The Canadian Task Force on Preventive Health
Care is an independent panel of clinicians and
methodologists with expertise in prevention, pri-
mary care, literature synthesis, critical appraisal and
the application of evidence to practice and policy.
The task force makes recommendations about clin-
ical manoeuvres aimed at primary and secondary
prevention. (Please see www .canadiantaskforce .ca
/members_eng.html for a list of current members of
the task force.)
Work on each recommendation is led by a
workgroup of two to five members of the task
force; a list of members of the workgroup for
the current guidelines is available at the end of
Recommendations on screening for breast cancer
in average-risk women aged 40–74 years
The Canadian Task Force on Preventive Health Care
Marcello Tonelli, Michel
Joffres, James Dickinson,
Harminder Singh, Gabriela
Lewin and Richard
Birtwhistle have received
support for travel to
meetings from the Public
Health Agency of Canada.
Gabriela Lewin is an
employee of Kemptville
District Hospital. No other
competing interests were
This article has been peer
Correspondence to: The
Canadian Task Force on
Preventive Health Care,
CMAJ 2011. DOI:10.1503
•The reduction in mortality associated with screening mammography is
relatively small for women aged 40–74 years at average risk of breast
A greater reduction in mortality is seen with mammography for
women at average risk aged 50–74 years than among similar women
aged 40–49 years; however, harms of overdiagnosis and unnecessary
biopsy may be greater for younger women than for older women.
When deciding whether to recommend mammography to a specific
patient, providers should first discuss the tradeoff between benefits
and harms, as well as the patient’s values and preferences.
For women at average risk who choose to have screening mammography,
an interval of every two to three years appears appropriate.
There is no evidence that screening women at average risk of breast
cancer using magnetic resonance imaging, clinical breast examination or
breast self-examination reduces the risk of mortality or other clinically
relevant adverse outcomes.
© 2011 Canadian Medical Association or its licensors
CMAJ, November 22, 2011, 183(17)1991
See related commentary by Gøtzsche on page 1957 and at www.cmaj.ca/lookup/doi/10.1503/cmaj.111721
this article. Each workgroup establishes the re -
search questions and analytical framework for
The Evidence Review and Synthesis Centre
(the details of which are available at www
.canadiantaskforce .ca /about _eng .html) as sembles
a team of methodologists who will perform the
systematic review, usually in conjunction with
one or more clinical experts. The team provides
input on the analytical framework, then summa-
rizes the evidence using a systematic re view
and quantitative summary of the relevant avail-
able evidence; narrative summaries are de -
veloped when quantitative synthesis is not fea-
sible. A list of members of the evidence review
team for the current guidelines is available at
the end of this article.
Once the systematic review is available from
the evidence review team, the task force work-
group independently develops the recommenda-
tion statements by consensus, based on a detailed
review of the evidence. In formulating recom-
mendations, workgroups consider both the bene-
fits and harms associated with a screening test,
patient values and preferences, the quality of the
evidence and, in some cases, the costs of the
intervention (Box 1). The strength of evidence is
determined using the Grades of Recommenda-
tion Assessment, Development and Evaluation
(GRADE) system.10The draft recommendations
as developed by the workgroup are revised and
approved by the entire task force.
Although members of a task force work-
group are not necessarily content experts in the
clinical area of the guideline, a content expert is
part of the evidence review team, and the re -
search questions, systematic review and recom-
mendations undergo internal and external peer
review by experts in the field and by stakeholders
and partners, such as the Canadian Breast Cancer
Screening Initiative for these guidelines. Details
about the task force’s methods can be found else-
where11and in Appendix 1 (available at www
.cmaj .ca /lookup /suppl /doi :10 .1503 /cmaj .110334
Key questions and analytic framework
for systematic review
The Breast Cancer Workgroup established key
questions and an analytic framework for the sys-
tematic review on screening for breast cancer
(Figure 2). Key questions were addressed by sys-
tematic review. Contextual questions (issues
judged not to require a systematic review, but that
were addressed by targeted literature searches)
are also shown in Figure 2.
Because previous guidelines have emphasized
the benefit of mammography for screening
women aged 50–69 years, the focus of the re -
view was women aged 40–49 years and women
aged 70 years and older; data were collected for
women aged 40 years and older. Randomized
and quasi-randomized controlled trials were
used to determine the effectiveness of screening
interventions (Figure 2, key questions 1a, 1b and
1c). Observational studies and mathematical
1992 CMAJ, November 22, 2011, 183(17)
Age group, years
Rate per 100 000 women per year
Events, number of women per year
30–3435–39 40–4445–49 50–54 55–5960–64 65–69 70–74 75–7980–84
Figure 1: Incidence of breast cancer and associated mortality among Canadian women in 2007. Sources:
Canadian Cancer Registry and Canadian Vital Statistics — Death Databases, Statistics Canada.
models were not used to assess efficacy owing
to their potential for bias and because there was
sufficient trial data to answer the key research
Randomized trials often fail to capture de -
tailed information on clinically relevant harms
and generally do not study patient values and
preferences. We used observational data to assess
these issues (Figure 2, key questions 2a, 2b and
2c, and contextual questions).
Because a high-quality systematic review
from the United States Preventive Services Task
Force10(a national organization with a mandate
similar to that of the Canadian Task Force on Pre-
ventive Health Care) had recently been published,
we chose to update their search to avoid duplica-
tion of effort. The previous summary of evidence
was used for evidence up to the end of 2008, and
an updated search for new evidence published
after that time was done by the evidence review
team. Because our initial search did not identify
sufficient age-specific data to assess the harms of
mammography, we did an additional search of
data from Canadian organizations including the
Public Health Agency of Canada and the Cana-
dian Institute for Health Information. The sys-
tematic review upon which the current guidelines
are based and an update as of October 2011 are
published on the task force’s website.12
A summary of the recommendations for clini-
cians and policy-makers is shown in Box 2.
More detailed explanations of the recommenda-
tions are available in Appendices 2 and 3 (avail-
able at www .cmaj .ca /lookup /suppl /doi :10 .1503
Women aged 40–49 years
For women 40–49 years of age, we recommend not
routinely screening for breast cancer with mam -
mography. (Weak recommendation; moderate-
Mammography is associated with significant
reductions in the relative risk of death from
breast cancer among women aged 40–49 years
(Table 1).13However, the absolute benefit is
lower for this age group than for older women
because of the younger group’s lower risk of
cancer. We calculated the number needed to
screen (NNS), defined here as the number of
women who would need to be screened about
once every 2 years over a median of about
11 years to prevent a single death from breast
cancer. Because not all women in the random-
ized trials who were invited to attend screening
actually had mammography, these NNS may
underestimate the absolute benefit of screening.
The NNS to prevent one death from breast
cancer for women aged 40–49 years is 2108, as
compared with 721 for women aged 50–
69 years. In addition, the risk of a false-positive
result from mammography is higher for women
younger than 50 years. Thus, screening about
2100 women aged 40–49 years once every 2–
3 years for about 11 years would prevent a single
death from breast cancer, but it would also result
in about 690 women having a false-positive
result on a mammogram, leading to unnecessary
follow-up testing, and 75 women having an
unnecessary biopsy of their breast.12
No primary studies looked at the risk of
overdiagnosis (diagnosis of breast cancer that
will not affect life expectancy or quality of life)
specifically among women aged 40–49 years,
but studies involving older women have esti-
mated that the frequency of overdiagnosis
ranges from 30% to 52%.12Data from our sys-
tematic review show that for every 1000 women
aged 39 years and older who are screened using
mammography, 5 will have an unnecessary
lumpectomy or mastectomy as a result of over-
diagnosis.12In addition to unnecessary interven-
CMAJ, November 22, 2011, 183(17) 1993
Box 1: Grading of recommendations
• Recommendations are graded as either strong or weak according to the
Grades of Recommendation Assessment, Development and Evaluation
system (GRADE).10GRADE offers two strengths of recommendation: strong
and weak. The strength of recommendations is based on the quality of
supporting evidence, the degree of uncertainty about the balance
between desirable and undesirable effects, the degree of uncertainty or
variability in values and preferences, and the degree of uncertainty about
whether the intervention represents a wise use of resources.
Strong recommendations are those for which the task force is confident
that the desirable effects of an intervention outweigh its undesirable
effects (strong recommendation for an intervention) or that the
undesirable effects of an intervention outweigh its desirable effects
(strong recommendation against an intervention). A strong
recommendation implies that most people will be best served by the
recommended course of action.
Weak recommendations are those for which the desirable effects
probably outweigh the undesirable effects (weak recommendation for
an intervention) or undesirable effects probably outweigh the desirable
effects (weak recommendation against an intervention) but appreciable
uncertainty exists. A weak recommendation implies that most women
would want the recommended course of action, but many would not.
For clinicians, this means they must recognize that different choices will
be appropriate for individual women, and they must help each woman
arrive at a management decision consistent with her own values and
preferences. Policy-making will require substantial debate and
involvement of various stakeholders. Weak recommendations result
when the balance between desirable and undesirable effects is small, the
quality of evidence is lower, and there is more variability in the values
and preferences of patients.
Evidence is graded as high, moderate, low or very low based on how likely
further research is to change our confidence in the estimate of effect.
tion, false -positive results can lead to fear, anxi-
ety and distress.14In the judgment of the task
force, this ratio of potential benefit to harm
does not justify routine screening in women
aged 40–49 years.
This recommendation places a relatively low
value on a very small absolute decrease in mor-
tality and reflects concerns with false-positive
results, the incidence of unnecessary biopsies
and overdiagnosis of breast cancer. The implica-
tions of a weak recommendation are that most
women would follow the recommended course
of action, but many would not. Clinicians should
discuss the benefits and harms with their patients
and must help each woman to make a decision
that is consistent with her values and prefer-
ences. Women who place a higher value on a
small reduction in mortality and are less con-
cerned about undesirable consequences are likely
to choose screening. Because it is likely that the
1994 CMAJ, November 22, 2011, 183(17)
Key questions (shaded circles)
1a. Does screening with mammography (film and digital) or MRI decrease mortality due to breast cancer and all-
cause mortality among women aged 40–49 years and ≥ 70 years?
1b. Does screening using clinical breast examinations decrease breast cancer mortality for women of all ages?
Alone or with mammography?
1c. Does breast self-examination decrease mortality from breast cancer for women of all ages?
2a. What are the harms associated with screening with mammography (film and digital) and MRI?
2b. What are the harms associated with clinical breast examinations?
2c. What are the harms associated with breast self-examinations?
1. What values and preferences related to screening for breast cancer do patients hold?
2. Are there subgroups of the Canadian population that have a higher burden of breast cancer or people for whom
it would be difficult to implement screening programs? Subgroup analysis that explores issues of burden of disease,
screening rates and special implementation issues include:
• Aboriginal women
• Women living in rural or remote locations
• Women from various ethnic backgrounds
3. What is the optimal frequency for screening using mammography?
4. What is the cost-effectiveness of screening for breast cancer?
People at risk
Women at average
risk, aged > 40 yr,
due to breast
Screening method, group
• Mammography (film and digital) or MRI, age 40–49 yr and ≥ 70 yr
• Clinical breast examination (alone and with mammography), all ages
• Breast self-examination, all ages
Figure 2: Analytical framework and key questions posed by the workgroup. MRI = magnetic resonance imaging.
benefit of screening increases in a continuous
fashion with increasing age (rather than a sharp
increase at 50 years of age), women aged 40–
49 years may be more inclined to receive screen-
ing as they grow older, even if their preferences
do not change.
Women aged 50–69 years
For women aged 50–69 years, we recommend
routinely screening for breast cancer with mam-
mography every two to three years. (Weak rec-
ommendation; moderate-quality evidence.)
Mammography is associated with significant
reductions in the relative risk of death from breast
cancer in this age group, and the absolute benefits
are greater than those seen among women aged
40–49 years (Table 1). The benefits of mammog-
raphy for women aged 60–69 years (NNS 432)
are greater than for women aged 50–59 years
(NNS 910). Screening about 720 women aged
50–69 years once every 2–3 years for about
11 years would prevent 1 death from breast can-
cer, but it would also result in about 204 women
having a false-positive result on a mammogram
and 26 women having an unnecessary biopsy of
their breast (Table 2).12In the judgment of the
task force, the larger absolute benefits for women
aged 50–69 years justify a weak recommendation
for screening, in contrast to the recommendation
for women aged 40–49 years.
The absolute benefits of screening remain
small among women aged 50–69 years, and a
substantial proportion of women will have false-
positive results on mammography leading to
unnecessary and invasive investigation. Again,
the potential benefits and harms of screening
should be discussed with each patient in the con-
text of her preferences. Women aged 50–69 years
who do not place a high value on a small reduc-
tion in mortality and who are concerned about
false-positive results, unnecessary diagnostic test-
ing and potential overdiagnosis of breast cancer
are likely to decline screening.
Women aged 70–74 years
For women aged 70–74 years, we recommend
routinely screening for breast cancer with mam-
mography every two to three years. (Weak rec-
ommendation; low-quality evidence.)
The reduction in relative risk of death from
breast cancer associated with mammography for
women aged 70–74 years is statistically non-
significant (Table 1). However, the point esti-
mate for relative risk is similar to that seen for
younger women, and the 95% confidence inter-
vals extend only marginally above unity. Given
the higher absolute risk in this age group, these
considerations suggest that the absolute benefits
of mammography are likely to be similar to
those seen among women aged 50–69 years.
However, patient preferences remain important
for determining who should and should not be
Screening about 450 women aged 70–74 years
once every 2–3 years for about 11 years would
prevent 1 death from breast cancer, but it would
also result in about 96 women having a false-
positive result on a mammogram and 11 women
having an unnecessary biopsy of their breast
(Table 2).12Women aged 70–74 years who do not
place a high value on a small reduction in mor-
tality and who are concerned about false-positive
results, unnecessary diagnostic testing and
potential overdiagnosis of breast cancer are
likely to decline screening.
Clinical considerations for women aged
The trials included in our review screened
women at intervals ranging from 12 to 33 months
(median 22 mo).15–21The optimal frequency of
screening cannot be determined at present, but
data from the sole randomized trial comparing
different screening intervals suggest no signifi-
CMAJ, November 22, 2011, 183(17)1995
Box 2: Summary of recommendations for clinicians and policy-makers
Recommendations are presented for the use of mammography, magnetic
resonance imaging (MRI), breast self-examination and clinical breast
examination to screen for breast cancer (see Box 1). These recommendations
apply only to women at average risk of breast cancer aged 40 –74 years.
They do not apply to women at higher risk because of personal history of
breast cancer, history of breast cancer in first-degree relatives, known
mutations of the BRCA1/BRCA2 genes or previous exposure of the chest wall
to radiation. No recommendations are made for women aged 75 years and
older, given the lack of data available for this group.
•For women aged 40–49 years, we recommend not routinely screening
with mammography. (Weak recommendation; moderate-quality
• For women aged 50–69 years, we recommend routinely screening with
mammography every two to three years. (Weak recommendation;
•For women aged 70–74 years, we recommend routinely screening with
mammography every two to three years. (Weak recommendation; low-
Magnetic resonance imaging
•We recommend not routinely screening with MRI scans. (Weak
recommendation; no evidence)
Clinical breast examination
• We recommend not routinely performing clinical breast examinations
alone or in conjunction with mammography to screen for breast cancer.
(Weak recommendation; low-quality evidence)
• We recommend not advising women to routinely practice breast self-
examination. (Weak recommendation; moderate-quality evidence)
1996CMAJ, November 22, 2011, 183(17)
Table 1: Summary of evidence of the benefits associated with using mammography to screen for breast cancer
Summary of findings
Deaths from breast cancer
Breast cancer mortality for ages 40–49 yr*
n = 152 300
n = 195 919
1 000 000
to 792 fewer),
Breast cancer mortality for ages 50–69 yr
n = 135 068
n = 115 206
1 000 000
to 2 050 fewer),
Breast cancer mortality for ages 70–74 yr
Serious*** No serious
n = 10 339
n = 7 307
1 000 000
Note: Estimates of relative risk are based on a random-effects meta-analysis. GRADE allows evidence to be rated as very low, low, moderate or high quality.
10 Randomized controlled trials begin as high-quality evidence,
whereas observational data begin as low. Evidence can be downgraded as a result of study limitations (e.g., lack of blinding or allocation concealment), inconsistency of results, indirectness of evidence, imprecision of
estimates (wide confidence intervals) or publication bias. Evidence can be upgraded if there is a large magnitude of effect, low likelihood of plausible confounding and a dose–response gradient.
13 CI = confidence
interval, GRADE = Grades of Recommendation Assessment, Development and Evaluation, NNS = number needed to screen (patients who need to be screened about once every 2 yr over a median of about 11 yr to
prevent 1 death from breast cancer), RR = relative risk.
*The available data were based on women aged 39–49 yr, although the focus of the review was women aged 40–49 yr. †Five quasi-randomized and three truly randomized trials. ‡Blinding and concealment were not clear for five studies; only three of them are considered truly randomized. §No heterogeneity exists; p = 0.48, I
2 = 0%.
¶The question addressed is the same for the evidence regarding the population, intervention, comparator and outcome.
**Total sample size is large and the total number of events is greater than 300 (a threshold rule-of-thumb value). ††Insufficient number of studies to assess publication bias. ‡‡Blinding and concealment were not clear for five studies; only two of them are considered truly randomized. §§No heterogeneity exists; p = 0.12, I
2 = 41%.
***Blinding and concealment were not clear. †††No heterogeneity exists, p = 0.75, I
2 = 0%.
‡‡‡Total sample size is large, but the total number of events is less than 300 (a threshold rule-of-thumb value).
cant difference between screening intervals of
one year and three years. However, that trial was
not adequately powered to detect a small benefit
of more frequent screening.22Pooled analyses
suggest that the effect of screening on mortality
is similar in trials with a screening interval of 24
months or more and those with a screening inter-
val of less than 24 months (Table 3). Further
stratified analyses suggested that the benefit of
screening appeared similar in trials with screen-
ing intervals of 33 months (two trials involving
98 431 women; relative risk [RR] 0.70, 95%
confidence interval [CI] 0.45–1.09),16,1824
months or longer (three trials involving 193 905
women (RR 0.77, 95% CI 0.58–1.03)16,18and
annually (four trials involving 311 165 women;
RR 0.87, 95% CI 0.77–0.99).15,17,20,21The small
number of women screened at intervals of
33 months did not permit further stratification by
age. Therefore, for women aged 50–74 years, we
suggest a screening interval of two to three
years, which appears to preserve the benefit of
annual screening but reduces adverse effects,
inconvenience to women and cost.
Since no studies show that the type of mam-
mography influences the anticipated reduction in
mortality associated with screening, either digital
or film mammography is acceptable.
Appropriate clinical actions following mam-
mography are outside the scope of this docu-
ment, but they are summarized elsewhere.23
Magnetic resonance imaging
We recommend not routinely screening for breast
cancer using MRI scans. (Weak recommenda-
tion; no evidence.)
There are no data evaluating whether screen-
ing women at average risk of breast cancer using
MRI scans reduces mortality as compared with
mammography or no screening. Thus, screening
women at average risk using MRI scans is not
CMAJ, November 22, 2011, 183(17)1997
Table 2: Estimated number of women with adverse outcomes following screening mammography
Women affected by age range, no.
Adverse outcome 40–49 yr 50–69 yr 70–74 yr
Per 1000 women screened
False-positive result on mammogram
Per single death prevented
Number needed to screen
False-positive result on mammogram
Note: Results are expressed per thousand women screened for a median of 11 yr (estimated as a total of 4 screening mam-
mograms per woman assuming a screening interval of 2–3 yr). The period of 11 yr was chosen because it was the approximate
median duration of follow-up during the randomized trials included in the systematic review. Data assume that rescreening rates
stay constant over time.
*Percutaneous or surgical biopsies of the breast that were subsequently found not to have cancer.
Table 3: Effect of screening with mammography on relative risk of death from breast cancer, stratified
by age and screening interval
Screening interval < 24 mo
Screening interval ≥ 24 mo
RR (95% CI)
RR (95% CI)
≥ ≥ ≥ ≥ 70
15,17–20 0.82 (0.72–0.94)
16,18 1.04 (0.72–1.50)
15,17–21 0.83 (0.76–0.92) High 3
16,18 0.77 (0.58–1.03) Low
Note: CI = confidence interval, GRADE = Grades of Recommendation Assessment, Development and Evaluation,
available, RR = relative risk.
*The evidence used to support this recommendation is based on data for women aged 39–49 yr.
†No trials performed in women aged ≥ ≥ ≥ ≥ 70 yr.
10 NA = not
We recommend not routinely performing clinical
breast examinations alone or in conjunction with
mammography to screen for breast cancer.
(Weak recommendation; low-quality evidence.)
We recommend not advising women to routinely
practice breast self-examination. (Weak recom-
mendation; moderate-quality evidence.)
No evidence was found to show that clinical
breast examination or breast self-examination
reduced mortality due to breast cancer or all-
cause mortality.24Two large trials identified no
reduction in breast cancer mortality associated
with teaching breast self-examination to women
aged 31–64 years, but evidence of increased
harm was seen (RR 1.5, 95% CI 1.1–1.9 for
benign finding on breast biopsy).25,26
Screening women aged 75 years and older
We did not identify data addressing the benefits of
screening mammography for women more than
74 years of age. It is possible that screening might
reduce breast cancer mortality in this group.
Given the small absolute reduction in mortality
associated with screening, benefit is unlikely
among people with limited life expectancy. Practi-
tioners should communicate this information to
patients so that it can be considered during joint
decision-making about whether to proceed with
Considerations for implementation
Screening with mammography leads to relatively
small reductions in mortality, together with
increased harm associated with false-positive
results and unnecessary interventions. Although
the absolute benefit of screening may increase
with longer follow-up, it remains relatively
small. There was no evidence that screening with
mammography reduces all-cause mortality.
Although screening might permit surgery for
breast cancer at an earlier stage than diagnosis of
clinically evident cancer (thus permitting the use
of less-invasive procedures for some women),
available trial data suggest that the overall risk of
mastectomy is significantly increased among
recipients of screening compared with women
who have not undergone screening.27
Although available data suggest that some
women would prefer to undergo screening despite
its potential harms, many would not.28–33These
data show that determining the preferences of
individual women about the relative importance of
potential benefits and harms is critical in deter-
mining who should undergo screening. Sources of
information for women should accurately portray
the value of mammography and the potential for
harm rather than simply provide encourage-
ment.7,34For example, the Public Health Agency of
Canada has created a leaflet to assist women with
deciding whether or not to undergo screening.35In
addition, one-page information sheets are avail-
able for both clinicians and patients to help with
shared decision-making (Appendix 3; additional
knowledge translation tools are available at
and at http://canadiantaskforce.ca/GRADE.html).
Introducing organized screening programs
appears to increase the proportion of women who
undergo mammography; such programs should
be structured to encourage women to make an
informed decision about whether to participate.
In some provinces, wo men may self-refer to or -
ganized screening programs; our recommenda-
tions are relevant to physicians advising their
patients about the po tential merits of mammogra-
phy within or outside of such programs. Re -
minders linked to an electronic medical record
might be helpful for in creasing the proportion of
women with whom the risks and benefits of
mam mography are discussed, but this would re -
quire further study.
Certain ethnic groups may have higher (e.g.,
Ashkenazi Jews)36or lower (East Asians)33risk of
death from breast cancer, which may alter the
absolute benefit of screening. Rates of screening
are low among Aboriginal populations,37,38
women with low incomes and recent immi-
grants;39further work is needed to explain these
findings and determine their potential impact.
Access to high-quality facilities with the neces-
sary equipment and expertise in mammography is
required for screening. Provincial and regional
decision-makers should consider whether access is
adequate for people in their jurisdictions who reside
outside of major centres. Mobile screening units
may help to increase access to screening among
women who live in rural or remote communities.
Suggested performance measures
An ideal performance measure for preventive ser-
vices would allow clinicians to assess the quality
of care that they are delivering to patients, and
allow the writers of guidelines to assess whether
their recommendations have influenced clinical
practice. The objective of these guidelines is to
improve health among women aged 40–74 years,
which requires balancing the potential benefits and
harms of using mammography to screen for breast
cancer. Although uptake rates of screening are
often used as performance measures, women aged
50–74 years who are well-informed might reason-
ably choose not to undergo mammography. There-
fore, performance measures based solely on the
1998 CMAJ, November 22, 2011, 183(17)
number or proportion of women in each age group
who undergo mammography may not be suitable.
For health care providers, the proportion of
women aged 40–74 years with whom the benefits
and harms of mammography are discussed is an
appropriate measure of performance. The propor-
tion of women aged 50–74 years who undergo
screening mammography at least every three
years could be used as a proxy for access to
screening services. However, the optimal propor-
tion of women who should undergo screening is
dependent on preferences and thus may vary
between populations. Measures of quality assur-
ance for facilities providing mammography
should be required routinely, including the evalu-
ation of the percentage of women screened who
are referred for further testing because of abnor-
mal results found with a program screen (i.e.,
abnormal call rate) and the number of women
detected as having invasive cancer during a rou-
tine screening episode per 1000 women screened
(i.e., invasive cancer detection rate).40
Economic implications of screening
Available data suggest that screening with mam-
mography every two years is associated with
costs per quality-adjusted life year that are gen-
erally considered to represent good value for
money in developed countries.41,42However,
many such analyses are based on observational
data, which may overestimate the potential bene-
fit of screening compared with trial data. Longer
screening intervals will be more economically
attractive than shorter screening intervals,
assuming that the benefit in terms of reducing
breast cancer mortality is retained, as the avail-
able evidence suggests.
The current guideline differs from previous rec-
ommendations made by the Canadian Task Force
on Preventive Health Care by lengthening the
screening interval from one year to two to three
years. Several other organizations have devel-
oped recommendations for screening for breast
cancer (Table 4).5,6,43–45The US Preventive Ser-
vices Task Force and the National Health Service
in the United Kingdom recommend routine
screening for women aged 50–74 years, but not
for women aged 40–49 years. The US Preventive
Services Task Force recommends screening for
CMAJ, November 22, 2011, 183(17)1999
Table 4: Comparison of recommendations for screening for breast cancer
Mammography, age range, yr
Organization 40–49 50–74
Care (1994; 2001),
Every 2–3 yr No
Every year for
women 50–69 yr
Every year for
women 50–69 yr
Every 2 yr Insufficient
against teaching to
Every 2 yr for
women 50–69 yr
3 yr until age 70 yr
Women > 70 yr not
Not recommended Not recommended
Note: NA = not available.
*Program is expanding to extend screening mammography every 3 years to women aged 47–73 yr.
women aged 50–74 years every two years,
whereas the National Health Service recom-
mends screening for women aged 50–70 years
every three years. The explanation for these dif-
ferences may be varying judgments about the
quality of available evidence.
The Canadian Task Force on Preventive
Health Care will update this guideline within
five years of publication.
Gaps in knowledge
Little is known about the benefit and harms of
screening using mammography for women older
than 74 years or younger than 40 years. New
technologies such as MRI scans have not been
adequately studied in the screening of women at
average risk. Digital mammography is a new
tech nology that is widely used in contemporary
clinical practice. The overall diagnostic accuracy
of digital versus film mammography as a means
of screening for breast cancer is similar, but digital
mammography is more sensitive and has similar
specificity for women younger than 50 years of
age, women with radiographically dense breasts
and premenopausal or perimenopausal women.46
Although improvements in technology sug-
gest that screening may be more effective now
than in the past, mortality among women with
breast cancer continues to decline (perhaps due
to better adjuvant treatment). It is possible,
though speculative, that the absolute benefit
attributable to screening might have declined in
parallel. Because all of the trials identified by our
review used film mammography, determining
whether digital mammography or MRI scan of
the breast improve the benefit associated with
screening (especially for younger women) would
require further randomized trials, which would
be of great interest to clinicians, patients and
We have recommended a screening interval of
every two to three years for women 50–74 years
of age using available evidence from randomized
controlled trials. The concept of individualizing
the interval for screening with mammography
based on breast density or other risk factors is
appealing but requires further study.47
Finally, given the importance of patients’
preferences for appropriate decision-making, fur-
ther studies are needed to determine the best way
to communicate information about the potential
benefits and harms of mammography.
Although screening mammography reduces mor-
tality from breast cancer among women aged
40–74 years, the absolute benefit is small —
especially for younger women — and is partially
offset by harms caused by unnecessary interven-
tion. Despite its potential to reduce mortality,
appropriate use of mammography will require
thoughtful discussion between clinicians and
patients about the balance between benefits and
harms. Finally, available evidence does not sup-
port the use of MRI scans, clinical breast exami-
nation or breast self -examination to screen for
breast cancer among women at average risk.
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Affiliations: From the Department of Family Medicine and
Community Health Sciences (Dickinson), University of Cal-
gary, Calgary, Alta.; the Departments of Internal Medicine
and Community Health Sciences (Singh), University of Man-
itoba, Winnipeg, Man.; the Department of Family Medicine
and Community Health and Epidemiology and the Centre for
Studies in Primary Care (Birtwhistle), Queen’s University,
Kingston, Ont.; the Department of Family Medicine, Univer-
sity of Ottawa, Ottawa, Ont. (Lewin); the Public Health
Agency of Canada (Joffres, Connor Gorber), Ottawa, Ont.;
and the Alberta Kidney Disease Network (Tonelli), Univer-
sity of Alberta, Edmonton, Alta.
Contributors: All of the authors made substantial contribu-
tions to the conception and design of the article, the acquisi-
tion, analysis and interpretation of data, drafted the article
and revised it critically for important intellectual content and
approved the final version submitted for publication.
Funding: Funding for the Canadian Task Force on Preven-
tive Health Care is provided by the Public Health Agency of
Canada and the Canadian Institutes of Health Research. The
views of the funding bodies have not influenced the content
of the guideline; competing interests have been recorded and
addressed. The views expressed in this article are those of the
authors and do not represent those of the Public Health
Agency of Canada.
Acknowledgements: The authors thank members of the
research team from the Evidence Review and Synthesis Cen-
tre who conducted the systematic review upon which these
recommendations were based, the staff at the Task Force
Office of the Public Health Agency of Canada, and the peer
reviewers whose thoughtful comments helped to improve the
quality of this manuscript.
Guidelines writing group: Marcello Tonelli, Sarah Connor
Gorber, Michel Joffres, James Dickinson, Harminder Singh,
Gabriela Lewin, Richard Birtwhistle.
Systematic review writing group: Donna Fitzpatrick-
Lewis, Nicole Hodgson, Donna Ciliska, Marcello Tonelli,
Mary Gauld, Yan Yun Liu.
CMAJ, November 22, 2011, 183(17)2001
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