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Senior Citizen Health & Medicine
Discovering How Environment Contributes to Breast
Cancer
Increase suggests that environmental
factors are primary causes
by Jeffrey Norris,
UCSF
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Robert Hiatt, MD, PhD,
principal investigator for the Bay Area BCERC |
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August 21, 2006 - Breast cancer incidence in the
United States ranks near the top internationally. And just across the
Golden Gate from the University of California, San Francisco ― in Marin
County ― studies show that the rate at which new breast cancers arise is
among the highest in the United States. Some Marin women touched by the
disease have been driven to activism. They are working with scientists
to plan and gain support for studies aimed at finding out why breast
cancer rates are so high.
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The trend toward increasing breast cancer incidence
in the United States is indeed disturbing ― even though increased
screening, early detection and better treatment have at the same time
produced a trend toward fewer breast cancer deaths.
Some breast cancer risk is due to genetics. For
instance, about 5 percent is due to rare mutations in just two genes
called BRCA1 and BRCA2. But the variability of breast cancer incidence
internationally and its overall increase over time suggest that
environmental factors are primary causes. Among immigrant populations to
the United States, for example, breast cancer incidence has increased
markedly in just one or two generations. The gene pool does not change
so quickly.
Environmental Exposures Are Not Limited to
Pollutants
The public and breast cancer advocates may think of
environmental toxins when they think of carcinogens. But to scientists,
environmental influences include not only toxicants, but also diet and
lifestyle.
Delayed childbearing is a lifestyle choice and a
growing trend. Putting off having children ― or never bearing children ―
is considered a reproductive risk factor. Reproductive risks increase
a womans exposure to her own estrogen. Estrogen clearly is an
important, beneficial hormone, but it also helps foster breast cancer.
Breastfeeding infants helps lower the risk. Other reproductive risks
that increase estrogen effects are early age of first menstruation and
late menopause ― not regarded as modifiable.
In addition to genes, breast cancer risks a woman
cant control include increasing age and a family history of breast
cancer.
Other known, modifiable breast cancer risks include
being overweight after menopause and taking hormone replacement therapy.
Alcohol consumption ― more than one drink per day ― also is a known risk
factor for breast cancer. A woman can lower her risk for breast cancer
by exercising. These modifiable risks all are considered environmental
factors.
Nationwide Collaborators Will Push Forward
Still, known risk factors only account for perhaps
half of breast cancers. UCSF and three other research institutions
nationwide now are leading a new research consortium to identify
additional environmental exposures that may increase breast cancer risk.
The Breast Cancer and Environment Research Centers
(BCERCs) are jointly supported by the National Institute of
Environmental Health Sciences and the National Cancer Institute. These
centers are unique in joining breast cancer advocates with academic and
other researchers. The other three BCERCs are led by the Fox Chase
Cancer Center in Philadelphia, Michigan State University and the
University of Cincinnati.
Epidemiological and laboratory research projects
are coordinated and procedures are standardized across sites, so that
the data may be more easily pooled or compared. Advocates play a key
role at all sites and are led by the Marin County Breast Cancer Watch at
the Bay Area BCERC. Advocates have been involved in designing the
studies, and they ensure that communication ― input and feedback ― flows
between researchers and members of the communities where the research is
being conducted.
Girls Are a Focus in Search for Cancer Causes
The epidemiologic focus of the research is on girls
who have not yet sexually matured. Mounting evidence indicates that
there is a window of vulnerability for breast cancer in adolescence.
Environmental exposures at the time of breast development can increase
the risk of breast cancer decades later. This has been observed in women
who received radiation therapy during childhood, in Japanese women who
were exposed to radiation from an atomic bomb blast as girls and in
laboratory mice exposed to chemical carcinogens prior to sexual
maturation.
In the Bay Area, 400 7-year-old girls will be
participating in the study. They are members of the Kaiser Permanente
Medical Care Program whose Division of Research in Oakland is a major
collaborator in the Bay Area BCERC. Their birth and past growth records
are available from medical charts. The girls will receive regular
checkups and be surveyed periodically about diet, exercise and other
factors that may affect exposure to breast cancer risks.
Lab studies of mice, carried out by UCSF
researchers and their collaborators at the Lawrence Berkeley National
Laboratory, will help researchers explore biological mechanisms that
might link environmental exposures to cancer, including exposures
identified as being of concern by community members and advocates.
A large part of the search effort will focus on
chemical exposures. Blood samples obtained from participating girls at
the four BCERCs are being evaluated for industrial contaminants
encountered in outdoor air, indoor air, water, food, food containers and
cooking utensils. Researchers are also tracking hormone levels. This
biomonitoring mirrors efforts begun in recent years by the Centers for
Disease Control and Prevention, which aims to track chemical exposures
in a representative sample of the US adult population.
The BCERCs were created as a result of continuing
public concern and lack of scientific evidence to convincingly confirm
or rule out a role for environmental chemicals in breast cancer,
according to Robert Hiatt, MD, PhD, principal investigator for the Bay
Area BCERC and director of population sciences for the UCSF
Comprehensive Cancer Center. The BCERCs are likely to contribute new
discoveries because of their unique focus on the determinants of
pubertal maturation, the interaction of laboratory and population
science, and the role of community advocates in the scientific process.
About UCSF
University of California, San Francisco is a
leading university that consistently defines health care worldwide by
conducting advanced biomedical research, educating graduate students in
life sciences and providing complex patient care.
Read more
Links:
>>
UCSF Comprehensive Cancer Center
>>
Breast Cancer and the Environment Research Centers
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