Day 036 - 13 Oct 94 - Page 37
1
2 Q. Can we just look at what Dr. Ip writes at the end of his
3 paper and that will take us, I hope, neatly to the right
4 time. Page 734, a section headed "Physiological Status of
5 the Host". "Previous studies with fat and mammary cancer
6 in experimental models have used young virgin rats which
7 are very sensitive to tumour induction. Animals are
8 normally given a single does of a carcinogen between 50
9 and 60 days of age, a window in their life span that is
10 particularly susceptible to malignant transformation of
11 the mammary gland.". Can we take it that that is what is
12 meant in the abstract by the words "carcinogen
13 administered at the time when the mammary gland is
14 exquisitely susceptible to tumour induction"?
15 A. Yes.
16
17 Q. "This could be the reason why the effect of fat is
18 'maximised' because the morphogenetic constitution of the
19 organ system at this stage predisposes to the induction of
20 neoplasia by exogenous factors. The question arises as to
21 whether the promoting effect of fat is, therefore, a
22 consequence of the characteristics of the model. In order
23 to collect some information in this area, we have examined
24 the effect of feeding a high-fat to rats which have
25 undergone a full-term of pregnancy and lactation.
26 Compared to the young virgin rats, these parous rats are
27 very resistant to carcinogenic induction of neoplasia of
28 the mammary gland." Do you want to make a comment?
29 A. Yes, thank you. It is important to recognise that
30 human mammary tissue is probably the most sensitive tissue
31 in the body, at least to certain types of carcinogens.
32 While it is quite reasonable to say that at some stages of
33 life that susceptibility is greater, perhaps even
34 substantially greater than in others, particularly as the
35 breasts are forming, there is, to my knowledge, no time
36 during life when breast tissue is not quite sensitive to
37 carcinogens. By "carcinogens" I do not mean simply
38 chemicals; I mean also radiation or other things that may
39 cause genetic damage.
40
41 This discussion that Dr. Ip is providing should not be
42 interpreted -- I do not see any evidence that he intends
43 this to be interpreted -- to mean that carcinogenic
44 induction is impossible later in life but simply -----
45
46 MR. JUSTICE BELL: He does not say that.
47 A. But simply that by comparison it is more difficult
48 later in life than early on, and compared to human mammary
49 tissue one might say is inducible at any age.
50
51 MR. RAMPTON: Dr. Barnard, with great respect to you, I believe
52 that some of what you said is represented here by what
53 Dr. Ip has said, but my belief is that what he is saying
54 is: Beware of previous studies that have proposed
55 tumourgenic effects or promotive effects of fat, because
56 in those studies the tendency has been to use virgin rats,
57 so that there has been deducted from the equation the
58 factor which may be thought to be important, pregnancy and
59 lactation?
60 A. Well, virgin rats are obviously not pregnant, and
