Day 017 - 25 Jul 94 - Page 48
1 influences of other important factors (e.g. genetic) in
the aetiology of large bowel cancers."
2
This in a sense is old ground for us, Dr. Arnott, because
3 we went over this some this earlier today. The question
I have since is 1990 when this was written, is there any
4 more certainty about this question than there was then?
A. Well, there is undoubted certainty as far as genetic
5 factors are concerned. Although one cannot necessarily
identify a specific genetic abnormality, we do see this
6 tremendous relationship between blood relatives and their
subsequent family and the incidence of large bowel
7 cancer. So if a blood relative has bowel cancer, then
subsequent relatives have a two to four times increased
8 risk of developing bowel cancer. There are of course the
other syndromes we mentioned this morning like polyposis
9 and these other syndromes associated with an increased
risk of large bowel cancer.
10
Q. So is the position this, that since this was written at
11 any rate one confounding factor genetic predisposition has
become stronger than it was?
12 A. I would say that is true.
13 Q. Continuing on page 600, "In 1971 Burkitt", that was the
study you referred to moment ago "suggested that the high
14 fibre diet in the South African Bantu might protect this
population from colorectal cancer by increasing the speed
15 of intestinal transit. This would reduce the exposure of
the gut to carcinogens. At the same time carcinogens
16 would be diluted by the greater bulk of the stool. The
link between fibre, transit time and colorectal cancer has
17 never been substantiated." In 1994 is that still the
position?
18 A. Yes. As I was saying earlier, although the other
study which you mentioned suggested it may be a factor, it
19 is a bit like the topics we were discussing this morning
that some studies suggest it may be a factor; other
20 studies give contrary evidence. It certainly has never
ever been substantiated. As it says here, we are going to
21 back to 1971 when Denis Burkitt first put forward this
theory.
22
Q. "Nevertheless, the dilutional effect of a bulkier stool
23 remains an attractively simple hypothesis, although
experimental models have produced conflicting findings."
24 Is that right?
A. That is absolutely right. As I was saying this
25 morning, these sorts of studies can only point one in
certain directions. They are observational studies. They
26 cannot necessarily provide a cause and effect
relationship. The experimental studies which have been
27 carried out to try to find out whether this is a real
relationship, have actually produced these conflicting
28 results.
29 Q. I am not going to take this very much further because
I think as far as I am concerned you have given us the
30 evidence we need to identify what I might call the
"certainty factor" in all this or one might call it the
