Drop in Breast Cancer Rates in Older
Women Directly Tied to Reduced Hormone Therapy
Women 50 to 69 had the
highest hormone use and the biggest reduction in
breast cancer when they stopped; women over 70 had parallel drop in
cancer
Senior Author
Karla Kerlikowske, MD
Nov.
30, 2010 In a massive study of over 2 million mammograms performed on
almost 700,000 U.S. women, scientists found a direct link between
reduced hormone therapy and declines in ductal carcinoma in situ (DCIS)
as well as invasive breast cancer. The researchers saw such a striking
decrease they believe they also have uncovered indirect evidence that
hormones promote breast tumor growth.
The
declines occurred in the age groups that most widely embraced then
abandoned hormone therapy, report the UCSF researchers.
For
nearly a decade, postmenopausal women have been strongly advised to
refrain from long-term hormone therapy or to use the lowest dose
possible for the shortest time to relieve hot flashes and night sweats.
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Numerous studies have suggested that women taking a combination of
progestin and estrogen faced a higher risk of breast cancer and other
potential health hazards.
The
new findings suggest that hormones helped promote breast tumor growth of
preexisting, clinically latent hormone-dependent cancers, not only
increasing the incidents of invasive cancer, but also the risk of ductal
carcinoma in situ (DCIS).
We
show that the incidence of breast cancer decreases if you take the
hormones away, said senior author Karla Kerlikowske, MD. The fact
that were continuing to see a decrease in invasive cancer means that
the effects of stopping the hormones may be long-lasting.
The
use of hormone therapy surged in the 1980s and 90s an estimated six
million American women found that the medications alleviated
postmenopausal symptoms. But at the same time, there was a steady
increase in the rate of breast cancer.
In
mid-2002, following a landmark report of the Womens Health Initiative
indicating that the risks of estrogen plus progestin therapy outweighed
its benefits, hormone therapy fell into widespread disfavor. Women by
the millions gave up hormones cold turkey or incrementally.
In the
new UCSF study, scientists reviewed 2,071,814 screening mammography
examinations performed between January 1997 and December 2008 on nearly
700,000 women between the ages of 40 and 79 as part of routine regular
screening mammography.
They
uncovered a clear pattern: women 50 to 69 years old had the highest
level of hormone usage and showed the biggest reduction in invasive
breast cancer when they stopped, from 40 cancers per 10,000 mammograms
in 2002 to 31 cases in 2005, 35 cancers in 2006. Likewise, rates of DCIS
markedly dropped in the same age group after hormone therapy ended.
There
was a parallel drop in cancer among women older than age 70.
Strikingly, the scientists found that among women 40 to 49 years old,
who were less likely to have been on hormone therapy, breast cancer
rates did not change over the course of the decade studied.
The
results corroborate previous declines in invasive cancer between 2000
and 2003 reported for women aged 50 to 69 by the same group of
scientists as well as other researchers. To the authors, the statistics
offer convincing evidence that hormone therapy cessation reduces breast
cancer risk.
The
scientists say major questions remain unanswered: does a halt in hormone
therapy correlate to a delay in the clinical detection of tumors,
leading to a short-term reduction in cancer rates, but not a long-term
drop? Do the effects apply long term for all tumors influenced by
hormone therapy?
The
study supports the idea that by giving the hormones we were promoting
tumor growths by giving the hormones, said Kerlikowske, professor of
medicine, and epidemiology and biostatistics at the UCSF Helen Diller
Family Comprehensive Cancer Center, and co-director of the Women
Veterans Comprehensive Health Center at SFVAMC.
When
the promoter is taken away, the incidence of breast cancer decreases.
While
scientists continue to investigate the relationship between hormones and
cancer, Kerlikowske said that using hormone therapy on a short term
basis is probably OK. But long term, it is not OK.
Co-authors are Ghada N. Farhat, PhD, San Francisco Coordinating Center,
California Pacific Medical Center Research Institute; Rod Walker, MS,
and Diana S.M. Buist, PhD, MPH, of the Group Health Research Institute,
Seattle; and Tracy Onega, PhD, Department of Community and Family
Medicine Dartmouth Medical School, Norris Cotton Cancer Center, Lebanon,
New Hampshire.
The
research was supported by the National Cancer Institute-funded Breast
Cancer Surveillance Consortium co-operative agreement.
UCSF
is a leading university dedicated to promoting health worldwide through
advanced biomedical research, graduate-level education in the life
sciences and health professions, and excellence in patient care.
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