=======================Electronic Edition========================
RACHEL’S HAZARDOUS WASTE NEWS #375
—February 3, 1994—
News and resources for environmental justice.
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CANCER DOWN ON THE FARM
The U.S. is losing its war on cancer, according to a long article
in the January, 1994 SCIENTIFIC AMERICAN. [1] The basic measure
of success or failure — the age-adjusted cancer death rate
— continues to climb slowly year after year, despite $25 billion
spent to find a cure since 1971 when Richard Nixon declared a
national “war on cancer.”
The cancer establishment–the largely male, largely white and
largely elderly group of researchers who act as gatekeepers for
cancer research dollars–try to put a good face on it. They
point to reductions in deaths from childhood cancers, reductions
in cancer deaths among young adults, and reductions in deaths
from some specific cancers. Still the fact remains that the
total age-adjusted death rate for cancer continues to climb year
after year. The rise in the cancer death rate is particularly
steep among people 65 and over.
The cancer establishment tends to blame cancer on individual
lifestyles, such as diets high in fat and low in fiber. There is
one major problem with this argument. Heart disease is known to
be associated with cigarette smoking, heavy use of alcohol, and
diets high in fat and low in fiber and low in antioxidants
[beta-carotene, vitamin E and selenium, for example]. In several
countries heart disease rates are decreasing. In the U.S., heart
disease is down 40% from its peak in the 1960s. It therefore
seems unlikely that recent increases in cancer are caused by the
same factors that cause heart disease.
Now a group of younger cancer researchers is advocating a return
to the fundamental principles of public health developed during
the 19th century, based on prevention. Much of cancer is thought
to be preventable because rates of occurrence and death vary
substantially from one population to another. Environmental
factors are likely to account for much of this variation.
Between 1969 and 1986, several cancers increased significantly
among persons aged 64 to 84 in six industrial countries. [2]
Multiple myeloma [cancer that starts in the bone marrow and
spreads to various bones, especially the skull], melanoma of the
skin, and cancers of the prostate, bladder, brain, lung and
breast are increasing in the general population of several
industrial countries. Except in the case of lung cancer, these
increases remain largely unexplained.
In the last two years, cancer prevention researchers have focused
new attention on environmental chemicals. Devra Lee Davis and
others have developed a hypothesis about the cause of breast
cancer in women. For a long time researchers have known that
exposure to estrogen (the female hormone) increases a woman’s
risk of breast cancer. Now Davis has shown that many fat-soluble
industrial chemicals, widely distributed in the environment,
mimic or amplify the biological effects of estrogen. [3] [See
RHWN #369.] The National Cancer Institute is now planning to
establish a laboratory to study “hormonal carcinogenesis”
(hormones as causes of cancer).
Now a second hypothesis has been developed by Devra Davis, Aaron
Blair, Sheila Hoar Zahm, Neil Pearce, Joseph Fraumeni, and others
at the National Cancer Institute, asking about the role of
pesticides in certain cancers. The hypothesis begins by
examining the health of farmers.
Two million farm workers, and three million farmers and their
families, form a large occupational group exposed to toxic
chemicals. [4] Farmers are a relatively healthy group. For any
given age, farmers have a low overall mortality rate, indicating
general good health. Compared to the general public, farmers
have lower risk for ischemic heart disease [narrowing of the
coronary arteries], and for all causes of cancer combined. [5]
Farmers also have lower risks for cancers of the lung, esophagus,
bladder, colon, liver, and kidney.
Low rates of cancer for lung, esophagus, and bladder, and low
rates of heart disease, can be explained by low prevalence of
smoking among farmers, which has been noted in numerous studies.
In addition, farmers have a low percentage of body fat, and a
high measure of physical fitness, probably because they perform
hard physical labor that keeps them in good shape. This good
physical condition probably contributes to lower risks for heart
disease and colon cancer, both of which are associated with a
sedentary lifestyle.
Farmers also eat a relatively large amount of fruits and
vegetables, compared to the average American, and relatively
small amounts of processed foods. As a consequence, farmers’
diets are most likely higher in fiber than the average diet.
Furthermore, in general, farmers reside in areas with little air
pollution.
However, despite their generally good health, farmers have
higher-than-general-population risks for certain cancers:
non-Hodgkin’s lymphoma, skin melanomas, multiple myeloma,
leukemia [cancer of the blood-forming organs], and cancers of the
lip, stomach, prostate, and brain.
These high rates of a few select cancers among farmers, against a
background of low risks for most cancers and for non-cancer
diseases, suggests that work-related exposures may be causing
specific cancers among farmers.
These patterns may have broad public health implications since
several of the high-rate tumors among farmers are the same
cancers that appear to be increasing in the general population of
many developed countries: multiple myeloma, non-Hodgkin’s
lymphoma, melanoma of the skin, and cancers of the prostate and
brain.
There are several factors that could be causing these cancers
among farmers: farmers are out in the sun a lot, and ultraviolet
sunlight is associated with melanoma and cancer of the lip.
Exposure to phenoxy herbicides (2,4-D, 2,4,5-T, acilfluorfen,
CNP, erbon, mecoprop, and others) has been linked to
non-Hodgkin’s lymphoma, and to soft tissue sarcoma. [6] Exposure
to insecticides has been associated with leukemia, multiple
myeloma, and brain cancer. It is possible that animal viruses
may play a role in some farmers’ cancers because elevated risks
of leukemia, soft tissue sarcoma, and non-Hodgkin’s lymphoma have
been seen in slaughterhouse workers and veterinarians.
But there is also another possibility. Perhaps something in the
environment damages the immune systems of farmers, who then fall
prey to cancers that healthy immune systems would have been able
to ward off.
It is noteworthy that the same cancers that affect farmers also
affect people whose immune systems have been damaged by disease,
or by medical intervention. Patients with AIDS (acquired immune
deficiency syndrome) experience striking excesses in
non-Hodgkin’s lymphoma. (However, the AIDS epidemic does not
provide a complete explanation for the increase in non-Hodgkin’s
lymphoma among the general population. The general increase
started before the AIDS epidemic began. In the U.S., the
greatest increases in non-Hodgkin’s lymphoma, multiple myeloma,
and leukemia have occurred in rural agricultural areas of the
central region of the country.)
People who have organ transplants are given drugs to suppress
their immune systems because the immune system would normally
reject a foreign organ; these people, too, have high rates of
non-Hodgkin’s lymphoma. Brain and skin cancers occur among bone
marrow transplant recipients; soft-tissue sarcomas, skin
melanomas, and squamous cell carcinomas of the skin and lip occur
in kidney transplant patients; leukemia and stomach cancers occur
in people with immunodeficiency diseases.
This similarity between cancers associated with immunosuppression
and cancers among farmers suggests that farmers’ cancers may be
caused by environmental factors that damage the immune system.
There is a large and convincing body of evidence showing that
pesticides harm the immune systems of laboratory animals. [7]
However, the number of human studies is very small. In humans,
pesticide exposures have been linked to a variety of immune
system effects including decreased host resistance to disease;
suppressed T-cell activity; enhanced B-and T-cell immune
response; and contact hypersensitivity. T-and B-cells are
particular kinds of cells that circulate in the blood and protect
the body by fighting off bacteria, viruses and cancer cells.
Increasingly, the general public is exposed to the same chemicals
that farmers are exposed to. And, as we saw last week, there is
evidence that immune disorders are increasing in the general
population. The hypothesis of Davis and her colleagues, that
chemicals (or other factors) on farms are increasing the cancer
rates among farmers, could have important consequences for us
all. It represents a new kind of tough, creative thinking that
has been missing from the war on cancer up until now.
                
                
                
                
    
–Peter Montague, Ph.D.
===============
[1] Tim Beardsley, “A War Not Won–Trends in Cancer
Epidemiology,” SCIENTIFIC AMERICAN Vol. 270 (January 1994), pgs.
130-138.
Descriptor terms: cancer statistics; mortality; morbidity; diet;
fat; fiber; antioxidants; heart disease; prevention; multiple
myeloma; melanoma; skin cancer; prostate; bladder; brain; lung;
breast; estrogen; agriculture; farm workers; farmers; smoking;
air pollution; sunlight; phenoxy herbicides; viruses; soft tissue
sarcoma; non-Hodgkin’s lymphoma; aids; organ transplants; immune
system; studies; hypotheses;