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.
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