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Environment
and Disease
Criticism of Animal
Tests
  There are problems in understanding and
using laboratory animal tests. Much of the public and, in fact,
a fair segment of the scientific community are reluctant to
put faith in laboratory animal tests. These people are uncomfortable
with the relationship between men and mice. Scientists often
debate the value and meaning of certain tests. It is important
to scientific study that theories are tested and retested and
not prematurely accepted. However, I think the relationships
and the concepts that laboratory animals predict for man are
quite good. There is empirical evidence from a variety of studies
that animals do predict for man, not only for cancer, but for
other forms and quantities of toxicity.
 Mammalian species, ranging from tiny mice
to enormous elephants, are very similar in their biological
function, physiology, and biochemistry. Such extensive similarities
have permitted us to learn much of what we know about human
physiology and biochemistry by the convenient and effective
study of laboratory animals.
Many people who are
unfamiliar with this type of research question the need to administer
large doses of chemicals to the animals in laboratory tests.
The amount of chemical used is related primarily to what we
call the statistical power of the animal tests. It is extremely
difficult to detect anything less than a very strong carcinogen
unless researchers use either an enormous number of animals,
hundreds of thousands, or larger doses and fewer animals. Negative
test results from small numbers of animals simply mean that
a chemical is not an extremely powerful cancercausing agent
or carcinogen.
 Animals are not unlike humans; nearly all
strains have some incidence of cancer in the general population.
This fact further complicates research results. After an animal
test is designed and chemicals are administered to the animals,
the scientists must decide which of the resulting cancers were
caused by the chemical and which might have been present as
the normal incidence. This decision poses severe statistical
problems.  The chance of detecting a two-fold incidence of cancer using 50 rats
is just 2 in 1,000, an almost infinitesimal chance of detecting
a cancercausing agent. By doubling the number of animals to
100 rats, there still is only a 2 in 100 chance of doubling
the background rate of cancer. Because of economics and resources
it is impossible to use thousands and thousands of animals.
The only other alternative is to use larger and larger doses
of the chemical being studied. These doses are not lifethreatening
per se; they do not cause other toxicities in the animal population,
but are simply larger doses.
Although there are
other reasons for using large doses, such as the fact that animals
excrete chemicals faster, the main reason large doses are necessary
and valid is due to the lack of statistical power, of a test
using only 50 or even fewer animals in each experiment.
  I have pointed out that the relationship between
disease in man and ir animals is good, but it certainly is not
perfect. This imperfect relationship often is a major criticism
of laboratory animal tests. I do not believe that this is a
valid criticism since we live in an imperfect world We have
learned to deal with such imperfection. For example, all of
us listen to the weather report and generally we believe it.
Most of the time the report is correct, but some of th time
it is not. However, we would much rather have the weather forecast
than have nothing at all.
Many people have
expressed the belief that everything causes cancer, that the
discovery of a new carcinogen is "nothing new." There are two
reasons for this pervasive feeling. The most important reason
is that cancer testing in laboratory animals began in earnest
only about 5 or 10 years ago. Since it takes about five years
to develop a full test, during the past three or four years
we have learned the results of the first largescale testing
of potentially cancercausing chemicals in our environment. We
are seeing a large number of positive reports. However, not
every chemical causes cancer. In the initial large-scale National
Cancer Institute study, scientists selected to study 120 compounds
which were suspected of being carcinogenic. Of these 120 specifically
chosen (not randomly chosen) compounds, less than 10 percent
were found to cause cancer.
In addition to using
animals for studying cancer, scientists at the National Institute
of Environmental Health Sciences and other institutions are
beginning to develop animal tests for other chronic diseases.
However, these tests are not as well developed as those for
cancer. It will take a number of years before we can discuss
these tests with the quantity of evidence that we have for cancer
tests.
 I believe that animal tests should be used
to study chemicals to see if they do cause cancer or other chronic
diseases. If the chemicals do cause diseases, we need to restrict
or control their use. Restriction does not always mean banning
a chemical. However, it does mean reducing exposure to minimize
the risk of developing disease. If we do that, we can control
some of these serious chronic diseases. Such control is an enormous
task because of the huge numbers of scientific, technical, logistical,
social and economic problems that must be addressed and solved.
Nevertheless, as a general principle, I suggest that we enter
into a partnership with laboratory animals and work to control
chronic diseases.
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