BREAST CANCER AND THE ENVIRONMENT: WHAT WE KNOW… WHAT WE SUSPECT… WHAT WE
CAN DO IN THE MEANTIME
Tuesday May 14, 2002, 7 PM in the Benedictine Hospital Senior Residence
Center, Kingston NY
The effects of the environment on breast cancer risk are controversial and
complicated. Dr. Devra Davis, Ph.D., M.P.H., is an internationally renowned
epidemiologist and toxicologist, and Professor in the H. John Heinz III,
School of Public Policy and Management, at Carnegie Mellon University.
has held presidential appointments, a number of distinguished visiting
professorships, and chaired several major international symposiums and
other professional activities.
Dr. Davis is also an advisor to the Benedictine Hospital Breast
Cancer/Pesticide Study started by Sheldon Feldman, MD several years ago.
On May 14, 2002 at 7PM, Dr. Davis discussed various environmental risk
factors of cancer, specifically when conclusive evidence is not available.
For more than three decades, scientists have consistently identified a
number of risk factors that are generally believed to account for up to 40
percent of all cases of breast cancer.
Among the established risk factors
for breast cancer are: having menstrual periods that begin before age 12
and end after age 55, having no children or bearing children late in life,
not nursing children, early and repeated exposures to relatively high doses
of radiation, obesity after menopause, and a family history of breast
cancer occurring in a close relative before age 40.
Other factors are
suspected of increasing risk, although the data are less clear. These
include: drinking alcohol daily, lack of vigorous exercise, low intake of
vitamin D and fiber, active and passive smoking, and living near chemical
However, while many risk factors have been suggested, not many
have been sufficiently ‘proven’ to merit elimination.
So, although certain risk factors for breast cancer, such as age at
menarche, diet, and genetic predisposition, have been well known for years,
many breast cancer cases occur in women with no known risk factors for
disease. Scientists cannot explain why there are more new cases of breast
However, a growing and complex array of evidence suggests
that the general external environment including behavior, diet, and
physical and chemical exposures plays a major role in fostering breast
cancer. The general environment can induce breast cancer by two distinct
mechanisms. Environmental exposures may damage genes directly or they may
affect the overall production of growth-regulating hormones, such as
estrogen, progesterone, and other such naturally produced substances
Abundant evidence exists that a woman’s cumulative exposure to estrogen
plays a role in increasing breast cancer risk. The longer a woman is
exposed to estrogen over the course of her lifetime, the greater her risk
for developing breast cancer.
Women who start menstruating at an earlier
age and enter menopause at a late age, for example, are more vulnerable to
breast cancer than women who are menstrual for a shorter period of time.
Reduction of estrogen by surgical removal of ovaries can lower cancer risk
substantially; breast-feeding, which lowers cumulative estrogen exposure by
disrupting regular menses, also reduces the risk of breast cancer somewhat.
In addition, women who have toxemia during pregnancy have lower hormone
levels. One recent study suggests that their daughters have a reduced risk
of breast cancer, possibly because their developing breast cells were
subjected to lower prenatal levels of circulating hormones.
Such evidence of the role of naturally occurring hormones in cancer risk
has led to the hypothesis that synthetic hormones could be involved as
well. Over the past three decades, several lines of evidence have converged
indicating that a number of commonly used synthetic compounds can modify or
mimic the actions of natural estrogen in the body. Some of these
hormone-mimicking compounds may be beneficial, such as those generally
found in plants and fish. In contrast, other hormone-mimicking compounds
appear to be generally harmful, such as those often found in pesticides,
plastics, and fuels. Experimental, wildlife, and some human studies have
found higher levels of some of these damaging compounds in organisms with
altered hormonal functioning or other health problems, including
developmental and behavioral defects These mechanisms would suggest that
strict measures ought to be taken to eliminate any bad xenohormones from
the environment, but this has yet to be achieved.
The Precautionary Principle
A new approach to thinking about environmental regulations and how we
evaluate and control exposures to toxic chemicals has been emerging over
the past few years. This approach, called the "precautionary principle,"
states that "when an activity raises threats of harm to the environment or
human health, precautionary measures should be taken even if some cause and
effect relationships are not fully established scientifically." Stated
differently, when significant risks to public health exist, efforts should
be made to reduce those risks, especially avoidable risks, even when
scientific knowledge is inconclusive. The precautionary principle shifts
the burden of proof from the general public to a proponent who creates a
public health or environmental risk. Instead of the public having to show
that they have been harmed, a proof that is virtually impossible because of
the lack of scientific information, a proponent has to prove that the
activity, process, or chemical exposure is harmless.
With regard to potential risk factors, Dr. Davis suggests that it is
"better to be approximately right than precisely wrong." It seems absurd
that we continue to expose ourselves to potential risk factors, merely
because we lack the "proof" necessary to eliminate them from the
environment. Rather, Dr. Davis suggested proactive policies such as the
promotion of workplace safety, pollution prevention, subsidization of
healthy agriculture, and integrated pest management. Through measures such
as these we cannot assure the elimination of cancer, but we can promote a
safer environment. Here, we can take positive steps towards encouraging a
healthy lifestyle and eventually eliminating the risk of cancer.
Thanks to Hope Nemiroff for this summary. More to come (possibly)
Devra Lee Davis' book
LINK to site with articles
(long-time environmental activist
Devra Lee Davis)
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