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Postmenopausal Women See No Increased Risk of Breast
Cancer with Estrogen-Alone
April 11, 2006 - Estrogen-alone hormone therapy
does not increase the risk of breast cancer in postmenopausal women,
according to an updated analysis of the breast cancer findings of the
Womens Health Initiative (WHI) Estrogen-Alone Trial.
(See related stories sidebar for links to new articles on
Estrogen use by postmenopausal and black women.)
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Related Stories |
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Estrogen May Increase Blood Clots in Postmenopausal
Women, Breast Cancer in Blacks
April 11, 2006 - Estrogen therapy may increase the
risk of venous thrombosis, the formation of blood clots in the veins,
among postmenopausal women who have had their uterus removed, according
to a study in the April 10 issue of the Archives of Internal Medicine,
one of the JAMA/Archives journals. Another study in this issue says
hormone therapy, including estrogen, appears to be associated with
increased risk of breast cancer among black women.
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The results contrast with the previously reported
WHI Estrogen plus Progestin Trial, which found an increase in breast
cancer over about 5 years among those taking combined hormone therapy.
The WHI is sponsored by the National Heart, Lung,
and Blood Institute (NHLBI) of the National Institutes of Health. The
new analysis is published in the April 12 issue of the Journal of the
American Medical Association.
Over an average of about 7 years of follow-up,
study participants taking estrogen had fewer breast cancer tumors than
those in the placebo group. Women in the estrogen group were diagnosed
with breast cancer at a rate of 28 per 10,000 participants per year
versus a rate of 34 per 10,000 participants per year in the placebo
group. The difference in rates of breast cancer (6 per 10,000) between
the groups was not statistically significant, meaning it could have
occurred by chance.
The new analysis also found that participants
taking estrogen had 50 percent more abnormal mammograms that required
follow-up and underwent 33 percent (747 compared to 549) more breast
biopsies. An abnormal mammogram does not necessarily signal cancer as
shown in this studys results.
Longer follow-up is needed to fully explain the
reduced number of breast cancers in women taking estrogen. However, this
new analysis does not alter the overall conclusion from the WHI that
hormones, including estrogen-alone and estrogen plus progestin, should
not be used for the prevention of chronic disease, said NHLBI Director
and WHI Director Elizabeth G. Nabel, M.D.
The findings still support
current recommendations that hormone therapy should only be used to
treat menopausal symptoms and should be used at the smallest effective
dose for the shortest possible time.
The WHI Estrogen-Alone Trial was stopped at the end
of February 2004 because of an increased risk of stroke and no
significant effect on heart disease. The trial also found that estrogen
increased the risk of blood clots in the legs, reduced the risk of hip
fractures and had no significant effect on colorectal cancer.
A separate
report on the WHI memory study found estrogen increased memory problems.
The WHI Estrogen Plus Progestin study was stopped in 2002 because of an
increased risk of breast cancer and because, overall, risks from use of
the hormones outweighed the benefits. The combination therapy increased
the risk for heart attack, stroke, and blood clots but also reduced the
risk for hip and other fractures, and colorectal cancer.
When the WHI Estrogen-Alone Trial findings were
published in April 2004, the effect on invasive breast cancer was
uncertain. At that time, 218 cases of breast cancer had been reported
among all estrogen study participants and there was no in-depth analysis
yet of the cancers. The new report provides a more detailed analysis of
237 invasive breast cancers and of the mammograms in the two study
groups.
The Estrogen-Alone Trial involved 40 clinical
centers and 10,739 generally healthy postmenopausal women ages 50-79 who
did not have a uterus. Estrogen-alone (without progestin) is only
recommended for women without a uterus; women with a uterus who take
estrogen have an increased risk of endometrial cancer, so they are now
advised to take estrogen combined with progestin.
Participants were
enrolled in the study between 1993 and 1998 with 5310 women assigned to
active estrogen (0.625 mg/day of conjugated equine estrogens) and 5429
assigned to placebo. About 35 percent of the women had used hormone
therapy prior to the study and about 13 percent were using hormones at
the time they enrolled, but they had to be off of hormones for at least
3 months prior to starting the trial.
Subgroup analyses found that women who had a low
risk of breast cancer no family history, no benign breast disease,
etc. had fewer breast cancers on estrogen, while those with higher
risk had more breast cancers on estrogen compared to placebo.
This finding underscores the need to individualize
treatment for menopause symptoms based on a womans medical history and
her risk profile, said WHI Project Officer Jacques Rossouw, M.D.
Women in the estrogen group tended to have larger
tumors that were likely to have spread to lymph nodes, a finding that
suggests estrogen might reduce the risk of smaller tumors but not larger
ones, or that smaller tumors are not diagnosed early due to changes in
breast tissue. Another subgroup analysis suggested that for participants
taking estrogen, ductal carcinomas that occur in the milk ducts of the
breast were reduced to a greater extent than lobular carcinomas, which
form in the glands where breast milk is made. It is unknown whether any
effects on breast tumors will persist over time.
According to Stanford Universitys Marcia Stefanick,
Ph.D., the studys lead author and chair of the WHI Steering Committee,
the study improves understanding of the role of estrogen therapy in
breast cancer, though more research is needed to explain the subgroup
findings. What is clear now is that, overall, postmenopausal women
without a uterus who choose to take estrogen-alone do not have an
increased breast cancer risk, at least over the first 7 years of
treatment. This is clinically relevant, but women who are taking
estrogen should also be aware that they will likely need more repeat
mammograms and more breast biopsies, she said.
Rossouw said more research is needed on the role of
progestin. Participants in the Estrogen-Alone and Estrogen Plus
Progestin trials began at the same level of risk for breast cancer.
According to Rossouw, the increased risk of breast cancer found in women
taking combined hormones may be due to the effects of progestin when
it is combined with estrogen.
Part of the National Institutes of Health, the
National Heart, Lung, and Blood Institute (NHLBI) plans, conducts, and
supports research related to the causes, prevention, diagnosis, and
treatment of heart, blood vessel, lung, and blood diseases; and sleep
disorders. The Institute also administers national health education
campaigns on women and heart disease, healthy weight for children, and
other topics.
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