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| Cristi Baker, a mammography technician in Breast Imaging at the Nellie B. Connally Breast Center, assists a patient undergoing a diagnostic mammogram. |
Cancer screening, admittedly, is often inconvenient and uncomfortable, but for years experts have argued that the trade-off is a lower risk of death. Indeed, the mortality rates for common cancers, such as breast and colon cancer, have declined since screening for these became more routine. However, even one of the “gold standards” of screening tests—mammography —has been caught up in a recent swirl of controversy as experts debate its true ability to prevent cancer deaths.
Mammography sits at the forefront of debates over cancer screening. Numerous
studies have shown that cancer-related survival is better among screened
women than among unscreened women, and experts have agreed for many years
that mammography saves lives. The controversy began in 2000 when a Danish
study questioned the validity of five of eight randomized trials supporting
mammography’s benefit. Even though subsequent reviews have found
that four of the five studies were not flawed, the debate still lingers
in one form or another. Because the “quality of evidence”
in many studies of mammography varies and their results are inconsistent,
even the National Cancer Institute has stated that “the existence
of [mammography’s] benefit is uncertain.”
In addition to overall efficacy, some of the issues raised involve false-positive
rates and unnecessary interventions, false-negative rates, the use of
mammography in younger women, overtreatment of ductal carcinoma in situ
(DCIS), and radiation exposure.
Every time a woman undergoes mammography, there is an 11% chance that
the result will be a false positive, which not only causes the woman to
experience unnecessary anxiety but
also can lead to additional, and costly, imaging studies and biopsies.
After 10 screenings, this risk increases to 50%. The good news is that
studies have shown that women who have had a false-positive screening
result are much more likely to adhere to a screening regimen. Alternatively,
10% to 30% of breast cancers present at the time of screening are missed
by mammography. If a breast symptom develops after a false-negative mammogram
result, both the woman and her physician may be less likely to evaluate
it properly.
The wisdom of screening women in their 40s, in particular, has been called
into question. Breast cancer tends to grow more rapidly in younger women,
but because their breasts are more radiographically dense, mammography
is more likely to miss cancer. Still, many believe there are benefits
to screening this population. “Even the most conservative estimate
is that you can cut down the risk of death by 20%,” said Aman U.
Buzdar, M.D., a professor in the Department of Breast Medical Oncology
at The University of Texas M. D. Anderson Cancer Center.
Another concern with mammography is the overtreatment of DCIS, which accounts
for 18% of all breast cancers and 30% of all mammographically detected
breast cancers. Countless women receive aggressive treatment for DCIS,
including mastectomy and further therapy with tamoxifen, even though many
cases of DCIS may never progress. “The question comes up, a lot
of these women might die of other causes, and this cancer might not become
invasive,” said Dr. Buzdar. “However, data from some studies
illustrate that if you excise it and don’t adequately treat it,
a number of times the cancer will come back. The recurrence rates are
as high as 27%. Out of those patients, over half the time that the cancer
comes back, it is actually invasive cancer. Unfortunately, we don’t
have any tests that we can run today and tell a woman, ‘You have
a DCIS; if you do nothing, you are going to live a normal life.’
So we offer therapy to all these patients.”
A final issue is that mammography exposes sensitive tissue to radiation.
Radiation exposure is a known risk factor for breast cancer; however,
for women over age 40, the benefits of annual mammography appear to outweigh
any risk from ionizing radiation. Despite these concerns, there is no
denying that mammography is beneficial for older women; it reduces the
breast cancer–related mortality rate by 20% to 30%. “There
is quite strong evidence to suggest that if mammography is applied adequately
and across the board, you can substantially cut the risk of death,”
said Dr. Buzdar.
Therese Bevers, M.D., an associate professor in the Department of Clinical
Cancer Prevention and director of the Cancer Prevention Center, whose
area of expertise is breast cancer prevention, agrees: “I think
that overall there is evidence of benefit for mammographic screening,”
she said.
Another common breast cancer screening technique that has come under fire
is breast self-examination (BSE). A Chinese study of 266,064 women found
that women who were taught how to perform BSE had the same breast cancer
mortality rates as other women. Several smaller studies have also shown
that BSE does not lower the risk of advanced-stage cancer or death.
“For BSE, I think the problem there has been a lack of understanding
of what the studies have shown,” said Dr. Bevers. “The study
did not show that BSE was not beneficial. The study showed that teaching
women a technique with which to do BSE was not beneficial. We don’t
need to spend money on shower cards because [women] don’t need the
reminder; they don’t need to have a special visual on how to do
it. They will find [a breast lump] without that visual or reminder. But
I personally think, and I think most experts agree, that women should
be involved in their health. They should know what their breasts feel
like and should report any problems.”
To encourage women to overcome their apprehension and doubts about breast
cancer screening, Dr. Bevers suggests that physicians let their patients
know that there are treatment options, including breast conservation therapy.
She also suggests that physicians take the initiative to schedule patients
for screening. “A lot of times, the patient will not say no if they
are already scheduled for it,” said Dr. Bevers.
Dr. Bevers and other researchers at M. D. Anderson are investigating new,
less-invasive techniques for breast cancer screening that could one day
improve patient compliance and screening accuracy. Dr. Bevers imagines
that in the future, using molecular epidemiology, researchers could identify
women who have certain markers for breast cancer through blood tests,
thus sparing those who do not from mammography. “We have the PSA
[prostate-specific antigen] test for prostate cancer screening. It would
be nice to have a similar type of blood test for women that would tell
us who would need a mammogram,” said Dr. Bevers.
In these studies, researchers are testing several biomarkers, including
lysophosphatidylcholine, which is similar to a biomarker being tested
for the early detection of ovarian cancer. Elevated levels in the blood
could show that a patient is at increased risk for breast cancer. Still,
the studies are very preliminary. “We would not ever be able to
implement something as a counterpart to or as a replacement for mammography
until we had done a large-scale clinical trial that followed women over
an extended period of time. We are still trying to get enough preliminary
data to say it is worthwhile to do in a larger population with specific
risks,” said Dr. Bevers.
M. D. Anderson Cancer Center Breast Screening Guidelines*
* Updated September
2003
For more information on this topic or for questions about M. D. Anderson’s treatments, programs, or services, call askMDAnderson at (877) MDA-6789.
Other articles in OncoLog, February 2004 issue:
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