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Patients Prescribed DES While Pregnant
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The
U.S. Department of Health and Human Services 1985 DES Task Force
concluded that the weight of evidence supports the conclusion that
women prescribed DES during pregnancy have a modestly increased
risk of breast cancer. The most definitive study to date adds weight
to the association between DES exposure for pregnant women and increased
risk of breast cancer. Based on the available data, it is possible
to estimate breast cancer risk for women prescribed DES while pregnant.
It appears that the risk of breast cancer is approximately 30% higher
than the risk for non-exposed women. The relative risk is approximately
1.3 (33). The absolute lifetime risk for breast cancer for women
prescribed DES while pregnant is 13.3%, compared to 10.2% in unexposed
women (33).
When discussing breast cancer risk with patients, it may be helpful
to compare risk associated with exposure to DES while pregnant to
other, more familiar, sources of increased risk. As an example,
the relative risk of breast cancer for women with a first degree
relative (mother, sister) with breast cancer is 2.1 (32).
It is important to note that although DES exposure and hormone
replacement therapy (HRT) are both associated with slightly higher
risks for breast cancer, studies to date have not found any interactive
risk between DES exposure and HRT (23).
The contribution of DES exposure during pregnancy to overall breast
cancer risk should be considered when weighing issues such as use
of hormone replacement therapy and the use of Tamoxifen to prevent
breast cancer. Like non-exposed women, women prescribed DES while
pregnant should be encouraged to obtain regular breast examinations
and mammograms as currently recommended by the National Cancer Institute
(www.cancer.gov)
or the American Cancer Society (www.cancer.org).
Hormone Replacement Therapy (HRT)
Although both taking DES while pregnant and HRT have been independently
associated with an increased risk of breast cancer, research has
not found an interactive effect of DES exposure and HRT (23). The
lack of an interactive effect means that the combination of exposure
to DES and HRT does not increase the risk of breast cancer beyond
the risk associated with either DES exposure or HRT alone. Also,
the risk of breast cancer for a woman with a first degree relative
(mother, sister) is greater than the modestly increased risk of
breast cancer from exposure to DES while pregnant or exposure to
five or more years of HRT (23,32).
Ongoing Breast Cancer Research Women
prescribed DES while pregnant appear to be at a modestly increased
risk of breast cancer, with most studies demonstrating a relative
risk of 1.3 (33). Studies to date have not found a statistically significant increased
risk of breast cancer among DES Daughters of all ages. However,
a recent study did find significantly increased risk among DES Daughters
over age 40 (RR 2.5) (184). Since this was the first study to identify
a link, further research is needed to confirm a link and to determine
if DES Daughters of other ages also have a greater risk of breast
cancer.
For a complete list of the numbered citations
on this page see DES References.
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