Risk begins to return to normal after women stop taking hormones
Researchers confirmed that a daily, combined dose of
estrogen and progestin increases breast cancer risk in post
menopausal women, but added that this risk begins to return
to normal about six months after women stop taking the
hormones.
The analysis was part of the National Institute of Child
Health and Human Development (NICHD) Women's Contraceptive
and Reproductive Experiences Study and appears in the
December, 2002 "Obstetrics & Gynecology". The majority
of the study's funding was provided by the NICHD. The
Centers for Disease Control and Prevention in Atlanta
contributed additional staff and computer support for the
study. The National Cancer Institute also provided
additional funding.
"It is reassuring that breast cancer risk begins to return
to normal six months after women stop combined dose
estrogen-progestin therapy," said Duane Alexander, M.D.,
Director of the NICHD. "Women, in consultation with their
physicians, need to make the most informed decision
possible. The study authors have provided them with one
more piece of important information."
The NIH Women's Health Initiative (WHI) trial was the first
large clinical trial to assess the risks and benefits of
continuous combined hormone therapy. (The release
describing the trial is available at www.nhlbi.nih.gov/new/press/02-07-09.htm.) Last
July, researchers stopped the WHI trial because the risk of
breast cancer and heart disease from combined hormone
replacement therapy outweighed its potential benefits.
In this form of therapy, women take a combination of the
hormones estrogen and progestin. Essentially, the hormone
estrogen relieves such symptoms of menopause as hot
flashes, night sweats, sleeplessness, and vaginal dryness.
When taken alone, however, estrogen also increases a
woman's risk for cancer of the uterine lining, or
endometrium. Combining estrogen with progestin virtually
eliminates the risk of endometrial cancer.
"In planning the NICHD study, we sought to learn as much as
we could about the risks associated with the various kinds
of hormone therapy," said Robert Spirtas, DrPH, Chief of
NICHD's Contraception and Reproductive Health Branch and
senior author of the study. "At the time, little
information existed on whether combined hormone therapy
posed the same risks as estrogen therapy alone."
In the WHI trial, women used continuous combined hormone
therapy and researchers monitored their health during the
course of the study. When it became clear that the women
were developing breast cancer at higher than normal rates,
the researchers stopped the trial. Because the study was
stopped only recently, the WHI researchers cannot tell yet
whether the women in the study face any increased risk of
breast cancer now that they stop taking the hormones.
In contrast, researchers for the NICHD study began by
questioning women who had been diagnosed with breast cancer
about their hormone use and other potential risk factors
for breast cancer. These women were then compared to a
similar group of women who had not developed breast cancer.
"Our data suggest a positive association between continuous
combined HRT and breast cancer risk among current, longer
term users," the study authors concluded. "Progestin
administered in an uninterrupted regimen may be a
contributing factor."
The current study enrolled women who had been diagnosed
with breast cancer between July 1, 1994 and April 30, 1998
at treatment centers in Atlanta, Detroit, Los Angeles,
Philadelphia, and Seattle. A total of 3823 postmenopausal
white and black women were analyzed for the study. In all,
the medical histories of 1870 women who had developed
breast cancer were compared to the histories of 1953 women
who did not have breast cancer.
The researchers found that women on continuous combined
therapy for 5 years or more were 1.54 times more likely to
developing breast cancer than other women their age not on
this form of therapy. The risk of breast cancer increased
the longer the women used this form of therapy. However,
six months after the women discontinued the combined
therapy, their risk of breast cancer began to return to
normal. This held true for women who took the hormones for
5 years or longer before stopping, as well as for women who
took the hormones for only about 6 months.
"The NICHD study also included former users, and our data
indicate that the increased risk associated with use of
continuous combined hormone therapy began returning to
normal about 6 months after the women stopped using them,"
Dr. Spirtas said.
The analysis also found that an alternate form of hormone
therapy, which involves taking the hormones separately, on
different days of the month, may not increase breast cancer
risk in this group of women. The alternate form of therapy,
sequential estrogen-progestin therapy, includes a number of
regimens in which patients take the hormone progestin only
for 5 to 14 days per month. Earlier studies have
indicated, however, that sequential estrogen-progestin
therapy may increase the risk for cancer of the uterine
lining, or endometrium. The increase in endometrial cancer
from sequential estrogen-progestin therapy is thought to be
less than the risk from taking estrogen alone.
Estrogen alone may be prescribed to women whose uterus has
been surgically removed, as these women no longer have a
risk of endometrial cancer. The NICHD study did not find
any additional risk of breast cancer in women who took
estrogen alone. A recent study by the NCI found, however,
that women taking estrogen alone may be at increased risk
for cancer of the ovary. (The NCI's release on this study
is available at http://newscenter.cancer.gov/pressreleases/Laceyovarian.html.)
A separate WHI study of estrogen alone in women who had a
hysterectomy before joining the WHI hormone program
continues unchanged because, at this point, researchers are
uncertain of the balance of risks and benefits of estrogen.
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