Women aged 40 to 49 don't need
breast cancer screening unless they have risk factors
for the disease, according to new screening guidelines
from the American College of Physicians (ACP). So what's
a doc to do? Despite this, the American Cancer Society
(ACS) is recommending more scans, in some cases - using
MRI, at that. Choosing the right approach to screening
remains a complex cost-benefit analysis, fraught with
concern over false-negatives and false-positives.
The ACP guidelines, published in
April 3 in Annals of Internal Medicine, represent
a step back from the most aggressive screening practices,
and move into line with current Canadian practice. Rather
than lay down hard rules, the guidelines suggest that
in this age group, patient and physician should decide
together if screening is needed, based on the individual
case.
Advocates of screening, confident
it's here to stay, can afford to take a more critical
look at the true costs and benefits. Screening expert
Dr Joan Elmore of the University of Washington writes
in an editorial accompanying the new guidelines: "We
should learn to live with smaller absolute benefits
and higher risks than originally hoped for."
FALSE
POSITIVES ARE A NEGATIVE
Benefits are least clear in the 40-49 age group. About
half of women, if screened annually from age 40-49,
could expect to see at least one false-positive in that
time, and perhaps 2,000 would face biopsy, estimated
Dr Elmore. "For every 10,000 women who receive regular
screening mammography starting at age 40, six of them
might benefit through a decreased risk for death due
to breast cancer. Yet even this modest benefit requires
multiple screening examinations and follow-up for all
10,000 women for more than a decade."
How burdensome is this? A meta-analysis
of 117 mammography trials, published in the same issue
of the Annals, found rates of false positives
of 20-56% after 10 mammograms.
Yet another meta-analysis in the
same issue, reviewing 23 mammography trials, found little
evidence that false positives discouraged women from
continuing screening. Oddly, the one exception to this
rule was Canadian patients, who tended to be put off
by false positives. American women reacted oppositely
— a false positive made them more likely to stick
with their screening program.
False positives are not the only
cost of screening. Other potential downsides are false
negatives, radiation risks, discomfort and overdiagnosis
of ductal carcinoma in situ.
It's perhaps asking a lot for patients
to weigh these costs and benefits when deciding whether
to undergo screening. Most have only the haziest idea
of their risk. Media stories of breast cancer tend to
focus on freakishly young cases, with the result that
women in their 40s typically overestimate by more than
20-fold their chance of dying of breast cancer within
a decade. They overestimate the risk reduction from
screening by a factor of more than 100.
Anyone questioning mammography
in the US faces a potential backlash. For those in the
public eye, appearing blasé about cancer is a
one-way ticket to the doghouse. A National Institutes
of Health panel studied screening for the 40-49 age
group 10 years ago, and reported insufficient evidence
to recommend for or against it. The panellists were
called into Congress for a dressing-down by senators
who promptly voted 98-0 to fund screening in that age
group.
Things in Canada are a little less
politically charged. The Canadian Cancer Society's (CCS)
guidelines already stipulate that among average-risk
women aged 40-49, the doctor and patient should reach
an individual decision on screening.
The Society's primary focus is
on increasing the screening rates in women aged 50-69,
where the evidence of benefit is clearest, says Heather
Chappelle, senior manager of cancer control policy.
"We're achieving screening rates of 34-61% around the
country, but that's some way short of what we'd ideally
like to see, around 70%," she says.
SAFETY
NET SCARCITY
But there are new guidelines out for these women too,
this time from the ACS. They are published in the Society's
own journal, CA: A Cancer Journal for Clinicians,
March/April issue. These guidelines stipulate that high-risk
women should be screening at 30, not just with mammograms,
but with MRIs.
MRIs give a fabulously clear image,
and support for their use comes from research published
last month in the New England Journal of Medicine,
which showed that in women who have newly diagnosed
cancer in one breast, MRI can find tumours in the other
breast that mammograms miss.
But an MRI image costs about 10
times as much as a mammogram, and the machines are rare
even in the States — surely too rare for routine
screening. The ACS recommendation was not well-received
by many doctors and patients' groups, who accused the
authors of lacking realism.
In Canada, where MRI availability
is even more constrained, such a recommendation isn't
on the horizon. "We don't think there is enough evidence
to recommend MRI for routine breast cancer screening,"
says Heather Chappelle of the CCS.
ON
THE RETREAT
Finally, to save the best breast cancer news for last,
a new study in the NEJM, April 19 edition, finds
that the recent decline in breast cancer incidence is
no flash in the pan but a strong and steady trend, particularly
in the 50-69 age group. The authors have no doubt as
to the cause: the abandonment of hormone replacement
therapy (HRT). The findings come on the same day as
a Lancet study blames excess British deaths from
ovarian cancer on HRT.
Not everyone agrees on the reason,
but nobody can dispute that breast cancer is at last
in retreat. Not just in the US, but also in Canada,
which this year will almost certainly register declining
incidence numbers in every age group, including, at
last, the 60-69 group. That's one set of figures that
no one will want to argue with.
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