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USA: Study Finds No Link Between Organochlorines, Breast Cancer
WASHINGTON, DC -- A seven year study of breast cancer clusters
on Long Island has found no link between the disease and exposure
to chemical pollutants known as organochlorine compounds.
But a
separate study found that high exposure to pollutants called
polycyclic aromatic hydrocarbons was linked to a modest increase in
risk of developing breast cancer.
The results were announced today in three separate papers
stemming from the Long Island Breast Cancer Study Project, one of
the largest and most comprehensive
environmental epidemiologic studies
ever undertaken to explore the environmental factors that may
trigger breast cancer.
Exhaust from diesel buses and other
vehicles contains polycyclic
aromatic hydrocarbons (PAHs), which some studies have linked to
increased risk of certain cancers. Photo courtesy EPA The
researchers found no increased rate of breast cancer among area
women who might have been exposed to organochlorine compounds such
as the pesticide DDT.
However, high levels of exposure to
polycyclic aromatic hydrocarbons (PAHs), found in cigarette smoke,
vehicle exhaust and certain foods,
appears to elevate women's risk of breast cancer by 50 percent in
New York's Suffolk and Nassau counties.
"The goal of this population based, case control study was to
determine whether breast cancer incidence in women in these two
counties was associated with exposures to
environmental contaminants," said
principal investigator Dr. Marilie Gammon, associate professor of
epidemiology at the University of North Carolina at Chapel Hill
School of Public Health. "What we observed did not support that
possibility strongly.
"
Teasing Out Cancer Causes
The Long Island study was ordered by Congress in 1993 in
response to reports of elevated breast cancer deaths in a number of
northeastern states. Though many of the cases can be traced back to
known risk factors, such as a
family history of breast cancer,
or having a first child at a later age, the reasons for the
remaining cases are unknown.
Congress ordered the National Cancer Institute to examine
"potential environmental and other risks
contributing to the incidence of breast cancer" in Nassau, Suffolk
and Schoharie counties in New York and in Tolland County,
Connecticut. The project now includes more than 10 studies
exploring different environmental factors, along with laboratory
research designed to help explain the development of breast
cancer.
Among the possible triggers for breast cancer under study are
exposure to contaminated drinking water, sources of indoor and
outdoor air pollution, including emissions from aircraft,
electromagnetic fields, pesticides and other toxic chemicals, and
hazardous and municipal wastes.
High PAH Exposure Increases Cancer Risk
PAHs were examined because these compounds are known to cause
breast cancer in rodents, and a few small human studies have
suggested a possible association between these chemicals and
increased risk of breast cancer. Women can be exposed to PAHs by
breathing in cigarette smoke, and exhaust from cars, trucks and
planes, and by eating grilled and smoked foods.
Starting in 1996, Gammon and her colleagues collected blood
samples from 1,508 women in Nassau and Suffolk counties who were
newly diagnosed with breast cancer, and a similar number of women
who did not have cancer.
The blood samples were checked for direct
evidence of exposure to organochlorine compounds and PAHs, both of
which leave traces in the body for months or years.
Study participants also completed a questionnaire, and at some
of the women's homes, researchers collected samples of house dust,
tap water and yard soil to test for organochlorine compounds and
PAHs.
Exposure to PAHs causes the chemicals attach to DNA, creating
compounds known as adducts. Women with the highest levels of PAH
adducts in their blood had a 50 percent greater chance of
developing breast cancer, the study found.
Compared to other known risk factors for cancer, a 50 percent
increase in risk is considered modest, the researchers note. For
example, smoking increases the risk of developing lung cancer by
900 percent to 1,000 percent, while a family history of breast
cancer increases risk by 100 percent to 200 percent.
In addition, only women with the highest adduct levels showed an
increased risk of cancer - lower levels, even levels higher than
average, were not associated with higher risk.
"These ambiguous findings shed some doubt on a clear cause and
effect association," Gammon said.
"The study team is continuing to
investigate this issue on Long Island through additional research
focused on the possibility of individual responses to environmental
exposures."
For example, some women may have stronger responses to PAHs
because of their higher levels of the hormone estrogen. Estrogen
boosts cell turnover, making it harder for the body to repair
damaged cells before they replicate and pass the damage to new
cells. Breast cancer victims are known to have more estrogen in
their blood on average than other women.
"We know too, for example, that if a woman's ovaries, which
produce estrogen, are removed before she is 35, her risk of breast
cancer drops by half," Gammon said. "Men, who have little estrogen,
rarely get breast cancer."
The increase in breast cancer risk associated with PAH was
restricted to women with breast tumors that were either estrogen
receptor and progesterone receptor positive or who were negative
for both, she said. This means the link was stronger for women with
cancers that are considered hormone sensitive, but the reason for
the link is unclear.
"Our findings with polycyclic aromatic hydrocarbons suggest that
women's individual responses to similar PAH exposures might be more
relevant to breast cancer development than the absolute amount of
PAH exposure," Gammon said. "A lot more work needs to be done to
sort out exactly what and how environmental exposures may promote
breast cancer."
No Link Between Organochlorines and Breast Cancer
The study focused on organochlorine compounds because smaller
studies had suggested that the pesticide DDT - an organochlorine
compound that has been banned in the United States since 1972 -
might be associated with increased risk for breast cancer.
The researchers looked at DDT and its metabolite DDE, chlordane,
dieldrin and polychlorinated biphenyls (PCBs).
PCBs are a family of
chemicals used in transformers, capacitators and other electrical
equipment. They are no longer used in new equipment, but because
they break down so slowly, many areas still have high levels of
PCBs in the environment.
The study found no evidence that organochlorine compounds are
associated with the elevated rates of breast cancer on Long Island.
However, the researchers say that it is possible that breast cancer
risk in some individuals may be associated with organochlorine
exposures because of individual differences in metabolism and
ability to repair DNA damage.
"Recent research by other investigators suggests that
organochlorine compounds may be related to the type of breast
cancer that has clinical characteristics that are associated with
worse survival. This is an important issue that we are continuing
to investigate among the women in our study," Gammon said.
Two previous, hospital based studies conducted through the Long
Island Breast Cancer Study Project also found no link between
exposure to organochlorine compounds and increased risk of breast
cancer.
More Work Ahead
While the current study did not identify specific environmental
factors as a cause for breast cancer on Long Island, it does
provide clues to help direct future studies.
For example, Dr.
Habibul Ahsan of Columbia University in New York and colleagues are
now examining whether certain common DNA variations, involved in
the biosynthesis and metabolism of estrogen and environmental
carcinogens, are associated with risk for breast cancer.
Gammon and Dr. Regina Santella of Columbia University are
examining the role of gene variants that influence the oxidative
stress of environmental contaminants.
Oxidative stress is a term
used to describe a type of cellular damage caused by the metabolism
of oxygen.
Meanwhile, Gammon and her colleagues are continuing to follow
the women who participated in the current study to determine
whether organochlorine compounds, PAHs and
lifestyle factors influence the
survival of Long Island women diagnosed with breast cancer. Other
studies in the Long Island Breast Cancer Study Project are looking
at possible links between breast cancer and electromagnetic fields,
hazardous waste sites, chemicals in drinking water and other
potential risk factors.
The current research, reported today in two papers in the
journal "Cancer Epidemiology, Biomarkers & Prevention," is also
available at: .
gov/cancerinfo/LIBCSP
Copyright Environment News
Service (ENS) 2002. All Rights
Reserved.
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