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#375 - Cancer Down On The Farm, 02-Feb-1994

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

=====

[1] Tim Beardsley, "A War Not Won--Trends in Cancer Epidemiology,"
SCIENTIFIC AMERICAN Vol. 270 (January 1994), pgs. 130-138.

[2] Devra Lee Davis, David Hoel, John Fox, and Alan Lopez,
"International Trends in Cancer Mortality in France, West Germany,
Italy, Japan, England and Wales, and the USA," THE LANCET Vol. 366, No.
8713 (August 25, 1990), pgs. 474-481.

[3] Devra Lee Davis and others, "Medical Hypothesis: Xenoestrogens As
Preventable Causes of Breast Cancer," ENVIRONMENTAL HEALTH PERSPECTIVES
Vol. 101 (October 1993), pgs. 372-377.

[4] Marion Moses, "Pesticide-Related Health Problems and Farmworkers,"
AAOHN [AMERICAN ASSOCIATION OF OCCUPATIONAL HEALTH NURSES] JOURNAL Vol.
37 (March 1989), pgs. 115-130.

[5] Devra Lee Davis and others, "Agricultural Exposures and Cancer
Trends in Developed Countries," ENVIRONMENTAL HEALTH PERSPECTIVES Vol.
100 (1992), pgs. 39-44. And: Aaron Blair and others, "Clues to cancer
etiology from studies of farmers," SCANDINAVIAN JOURNAL OF WORK,
ENVIRONMENT AND HEALTH Vol. 18 (1992), pgs. 209-215.

[6] See studies of farmers and others reviewed in the Institute of
Medicine's study, VETERANS AND AGENT ORANGE: HEALTH EFFECTS OF
HERBICIDES USED IN VIETNAM (Washington, D.C.: National Academy Press,
1993).

[7] P.T. Thomas and others, "Immunologic Effects of Pesticides," in
Scott R. Baker and Chris F. Wilkinson, editors, THE EFFECTS OF
PESTICIDES ON HUMAN HEALTH (Princeton, N.J.: Princeton Scientific
Publishing, 1990), pgs. 261-295.

Descriptor terms: cancer statistics; mortality; morbidity; diet; fat;
fiber; antioxidants; heart disease; prevention; multiple myeloma;
melanoma; skin cancer; prostate cancer; bladder cancer; brain cancer;
lung cancer; breast cancer; 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;