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Senior Citizen Health & Medicine
Decline in Breast Cancer Likely Linked to Reduced
Use of Hormone Replacement
Since based on
population statistics, researchers not certain why the decline
December 15, 2006 - In 2003, the number of new
breast cancer cases in the United States dropped sharply, and this
decline may largely have been due to millions of older women deciding to
stop using hormone replacement therapy (HRT) in 2002. The investigators
found an overall 7 percent relative decline in breast cancer incidence
and that the steepest decline - 12 percent - occurred in women between
ages 50-69 diagnosed with estrogen receptor positive (ER-positive)
breast cancer.
This is the kind of breast cancer that is dependent
on hormones for tumor growth.
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From this, the researchers conclude that as many as
14,000 fewer women were diagnosed with breast cancer in 2003 than in
2002, a year in which the American Cancer Society estimates 203,500 new
cases of breast cancer were diagnosed.
This new analysis was led by researchers at The
University of Texas M. D. Anderson Cancer Center and presented at the
29th annual San Antonio Breast Cancer Symposium,
"It is the largest single drop in breast cancer
incidence within a single year I am aware of," says Peter Ravdin, M.D.,
Ph.D., a research professor in the Department of Biostatistics at M. D.
Anderson.
"Something went right in 2003, and it seems that it
was the decrease in the use of hormone therapy, but from the data we
used we can only indirectly infer that is the case," he says.
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"[T]he decrease in
use of hormone replacement therapy that followed publication of
the Women's Health Initiative in mid-2002 could have contributed
to the reduction in the overall female breast cancer incidence
rates between 2002 and 2003, although it is too early to know
for sure."
American Cancer Society epidemiologist Ahmedin Jemal, PhD |
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"But if it is true, the tumor growth effect of
stopping use of HRT is very dramatic over a short period of time, making
the difference between whether a tumor is detected on a mammogram in
2003 or not," says Ravdin.
The study's senior investigator, Donald Berry,
Ph.D., professor and head of the Division of Quantitative Sciences at M.
D. Anderson, says he was, at first, very surprised by both the magnitude
and the rapidity of the decline in incidence, but adds "it makes perfect
sense" if you consider that use of HRT may be an important contributing
factor to breast cancer development.
"Incidence of breast cancer had been increasing in
the 20 or so years prior to July 2002, and this increase was over and
above the known role of screening mammography," he says.
"HRT had been proposed as a possible factor,
although the magnitude of any HRT effect was not known. Now the
possibility that the effect is much greater than originally thought all
along is plausible, and that is a remarkable finding."
HRT provides both estrogen and sometimes also
progestin hormones to women who are postmenopausal. The ongoing Women's
Health Initiative study of 16,608 women 50-79 years old using HRT was
prematurely stopped in July, 2002 when the combination of estrogen and
progestin was found to significantly increase the risk of developing
invasive breast cancer.
Ravdin said about 30% of women older than 50 had
been taking HRT in the early years of this decade, that about half of
these women stopped using HRT in late 2002 after the results of the
large study were announced.
"Research has shown that ER-positive tumors will
stop growing if they are deprived of the hormones, so it is possible
that a significant decrease in breast cancer can be seen if so many
women stopped using HRT," he says.
"It takes breast cancer a long time to develop, but
here we are primarily talking about existing cancers that are fueled by
hormones and that slow or stop their growing when a source of fuel is
cut," Berry adds. "These existing cancers are then more likely to make
it under mammography's radar."
But the researchers stress that because the
analysis is based solely on population statistics, they cannot know for
certain the reasons why incidence declined.
"We have to sound a cautionary note because
epidemiology can never prove causation," he says. They considered
whether other effects may be involved (such as decreased use of
screening mammography and changes in the use of anti-inflammatory
agents, SERMs or statins) but only the potential impact of HRT was
strong enough to explain the effect."
To conduct the study, Ravdin, Berry, and
researchers at the National Cancer Institute (NCI) and Harbor UCLA
Medical Center analyzed data from nine regions across the country that
contribute data to the NCI's Surveillance Epidemiology and End Results
(SEER) database, from which national cancer incidence statistics are
derived.
They examined rates of breast cancer in the United
States from 1990 to the end of 2003 and found that while incidence
increased at 1.7 percent per year from 1990 to 1998, it began to
decrease, relative to other years, 1 percent each year from 1998 to
2002.
When that 1 percent increase was adjusted for age
in each of those years, incidence from 1998 to 2002 stayed about the
same, Ravdin says. "There were more cases of breast cancer being
diagnosed, but that was because women were getting older and entering
the higher risk pool."
But by the end of 2003, there was a 7 percent,
age-adjusted decrease in the number of breast cancer cases diagnosed.
With further analysis, the researchers discovered that decline in
incidence was far greater in ER-positive breast cancer (8 percent)
compared to ER-negative breast cancer (4 percent).
And when they looked at women 50-69 years old, the
decline in ER-positive cancer was 12 percent, compared to 4 percent in
ER-negative breast cancers. After adjusting for age, the researchers
concluded that there was an absolute decline of about 14,000 fewer women
diagnosed with breast cancer in 2003 than in 2002.
The study was funded by grants from the National
Cancer Institute and from M. D. Anderson.
Coauthors also include Kathy Cronin, Ph.D., and
Nadia Howlader from the National Cancer Institute, and Rowan Chlebowski,
M.D., Ph.D., from Harbor UCLA Medical Center.
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