Day 256 - 04 Jun 96 - Page 63


     
     1
     2   Q.   I assure you, Professor, from where I stand, there
     3        certainly is.
     4
     5        Take animal studies as a starting point.  What are the two
     6        most commonly used carcinogens in animal studies for
     7        mammary tumours?
     8        A.  It is usually the dimethyl benzanthracene hydrocarbon
     9        or the nitroso-methylurea, although there are also a
    10        significant number of studies where nothing was used,
    11        simply so-called spontaneous tumours were examined, and the
    12        same results were obtained.
    13
    14   Q.   Another one is azoxymethane?
    15        A.  Yes.  That has not been used really that much, to my
    16        knowledge.
    17
    18   Q.   Dimethyl benzanthracene, or DMH, has often been used, has
    19        it not?
    20        A.  That is mostly used in colon cancer, although I think
    21        you may be correct.  I am not sure about the mammary
    22        tumours.  The two principal ones, as I say, is dimethyl
    23        benzanthracene, DNBA; that is easily the most common one
    24        that has been used; and the second most common one is
    25        nitrozo-methylurea, NMU -- are the two acronyms.
    26
    27   Q.   Is not one of the problems -- are not several of the
    28        problems of animal experts these, that they are very useful
    29        for studying mechanisms in tumour promotion, but that they
    30        are telescoped in point of time, a bit like a mushroom
    31        growing up overnight, for these reasons:  first of all, the
    32        carcinogens are known to produce tumours which respond to
    33        overdoses of fat -- yes?
    34        A.  No.
    35
    36   Q.   No?
    37        A.  Not to my knowledge.
    38
    39   Q.   Secondly, that the genetic strains of rodent -- which are
    40        usually rats -- which are used in these experiments are
    41        pure bred and, therefore, prone to produce mammary tumours
    42        of their own accord?
    43        A.  That is not true, either.
    44
    45   Q.   No?
    46        A.  No.  Some of these inbred screens do have higher rates
    47        of certain kinds of cancers than, let us say, non
    48        (inaudible) strains, but one cannot draw a general
    49        conclusion from all the different kinds of tumours and
    50        different kinds of strains. 
    51 
    52   Q.   Third (though this may be less important), that the effect 
    53        observed in these animal experiments is that of tumour
    54        promotion, not initiation?
    55        A.  That is true, which is the most important part.
    56
    57   Q.   I understand.  That is right?
    58        A.  That is what makes it so impressive, the dietary fat
    59        effect.
    60

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