Women in the United States are not properly informed about the benefits
and risks of mammography and therefore are not able to make an educated
decision about whether or not to have the breast cancer screening performed,
according to a new study.
Study lead author, Dr. Lisa M Schwartz and colleagues
with the Veterans Affairs Medical Center in White River Junction, Vermont,
found of particular interest that only 6% of women were
aware of a form of usually non-progressive breast cancer known as "ductal
carcinoma in situ" (DCIS). However, once informed
that mammograms may detect these cancers that may never progress, "60%
of women wanted to take into account the possibility of it being detected
when deciding about screening.
Researchers did find that most women were aware
of false positive mammogram results and viewed them as an "acceptable
consequence" of mammography.
The authors conclude that "most
women are unaware that screening can detect cancers that may never progress
but think that such information would be relevant. Education
should perhaps focus less on false-positive results and more on the less-familiar
outcome of the detection of ductal carcinoma in situ."
However, an accompanying editorial goes even further,
saying that women are even less informed than this study would suggest.
In their opinion, Dr. Karla Kerlikowske and Dr.
Virginia L Ernster of the University of California, San Francisco (UCSF)
School of Medicine, state that:
It is not clear, however, whether the authors
accurately assessed women's true tolerance of false-positive mammography
results because their survey did not describe the spectrum of physical
and psychological sequelae of a false-positive result (for example,
additional diagnostic evaluations and associated morbidity and anxiety).1,2,3
Thus, the proportion of women
who are tolerant of false-positive mammography results may
have been overestimated because the possible harms of screening
mammography were not fully described. Even so, 38% of women
surveyed indicated that they would want to factor information about
the consequences of false-positive results into their decision about
undergoing screening mammography. If nearly 2 of every
5 women desire such information, then they should
be informed of the possible harms, as well as the benefits, of
screening mammography.
The editorial notes that the study by Schwartz et
al "found that a significant proportion (55%) of women overestimate
the benefit of mammography," yet the authors "conclude that
the high tolerance for false-positive results is not explained by overly
optimistic beliefs of the benefits of mammography." However, Kerlikowske
and Ernster think that it is possible that women do overestimate the benefit
of screening and that these misperceptions may explain why many women
did not want to factor information about the consequences of false-positives
into their decision about screening mammography.
They also note that:
... few women (6%) were knowledgeable
about ductal carcinoma in situ (DCIS). When women were informed about
DCIS, 3 of every 5 women wanted to take into account the chance of it
being detected when deciding whether to undergo screening mammography.
This is an important finding and suggests that information about DCIS
should be included in educational materials and discussions about the
possible benefits and harms of screening mammography.
Kerlikowske and Ernster note that some important
information that could be conveyed to women is the absolute benefit of
detecting DCIS. "For example, for every 10,000 women aged 70 years and older screened for 10 years, 65 cases of DCIS
will be detected and surgically treated with mastectomy or lumpectomy
and only 1 death from invasive breast cancer averted,"
they note.
The editorial concludes that:
To encompass a range of individual preferences,
women should be provided with estimates-in absolute terms-of the possible
benefits and harms of mammography to make an informed decision about
screening. Women who easily tolerate the additional tests that are recommended
following an abnormal screening result and want to do everything possible
to decrease the chance of death from breast cancer, even if certain
harms are involved, will likely choose to undergo screening mammography.
On the other hand, women who feel that the
small incremental risk of breast cancer death associated with not being
screened is outweighed by the fairly high likelihood of a false-positive
result, the additional testing, and the anxiety may rationally choose
not to have screening mammography.
Kerlikowske and Ernster recommend that the following
information be provided to a woman for informed decision making before
mammography:
- Individual risk of invasive
breast cancer and DCIS
- Age-specific
chance of an abnormal result
- Age-specific chance of a false-positive
result
- Chance that
mammography may miss cancer
- Expected absolute reduction in risk
of breast cancer deaths among women
in her age group who undergo screening mammography compared with women
who do not undergo screening
Western Journal of Medicine
2000; 173: 307-312, 313-314
For additional information about ductal carcinoma
in situ (DCIS) go to http://mammography.ucsf.edu/inform/index.cfm