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

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