Joint International Conference on Long-term Experiments ...

different tumor types does not help. In fact, because of multiple testing we have to adjust the
nominal p value and make the test even less powerful. Since the individual animal is the unit
of experimentation, the greatest power can be gained by using the entire pattern of lesions
seen in a given animal and by using only one or two hypothesis tests for the entire sex X
species experiment.
The appendix describes a method of multivariate analysis that does it. General
multivariate methods foe analyzing chronic toxicity studies can be found in Salsburg. The
specific method described in the Appendix was applied to six AZO dyes, whose bioassays
took place at the same site during the same period of time, and these analyses are discussed
in the next section.
If the Paracelsean thought experiment is correct, and with it the hypothesis that any
treatment has an effect, then a powerful statistical test should detect a significant treatment
effect in almost all studies – “almost all” because no statistical test has 100 % power.
B. Constructing Additional Studies to Test the Hypothesis
Statistical tests that show a shift in tumor patterns for all or almost all compounds, sexes,
and species in these studies provide strong evidence in favor of the hypothesis. However,
scientific hypotheses are not necessarily proven by the reanalysis of old data. We usually try
to construct new experiments that provide an opportunity to refute the hypothesis.
We can construct such studies by taking compounds that appear to show a complicated
shift in tumors and trying to find the biochemical or tissue changes that occur as a result of
treatment. We have to be careful to recognize that this is a very general hypothesis, and we
should not restrict the search for changes in milieu to specific hormones or to specific
histopathological events. We also have to be careful that such studies are used primarily to
examine the validity of the Paracelsean hypothesis. If, for instance, we find a set of changes
that seem to be associated with one class of chemical compounds, and if that class tends to
be mutagenic or ‘carcinogenic” in other models, we cannot assume that we have found
marker or proximate events unique to that class, and far more work will be needed to
establish such findings as indicative of that class. I propose a set of experiments of
following type: We pick 10-20 of the compounds that have shown paradoxical shifts in
tumors in the NCI/NTP program (increase in tumor incidence for one type of tissue
associated with decreases in tumor incidence of another type of tissue, where the
paradoxical events may be in different sexes or species). Using the same doses and the same
strains of animal, we redo the feeding study for a small number of animals over a relatively
short period (1-3 months). At the end of this time, we sacrifice the animals and examine the
target tissues (tissues in which paradoxical tumor increases or decreases have occurred).
The hypothesis predicts that we will find differences in “milieu”. There are rough tools
for comparing general patterns of proteins or fragments of active agents between two sets of
tissue, which have been used in the primary screening of undifferentiated biological
products where we are looking for something “new”. It would not be necessary to identify
these differences. It should be sufficient to show that there are discernible differences. If
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