Day 017 - 25 Jul 94 - Page 06

     
     1        promotion and therefore moving the cell further along the
              line to the development of a cancer can be reversed.  It
     2        is not an irreversible process.
 
     3   Q.   Can I understand this?  If there is an exposure which is
              promoting the progress of an initiated tumour, or whatever
     4        it may be?
              A.  It is just a cell at this stage; the tumour comes
     5        later on.
 
     6   Q.   This is my fault; I am not a scientist, as you probably
              appreciate.  Could it be that simply the removal of that
     7        particular exposure might inhibit or halt the promotion?
              A.  Undoubtedly, yes.
     8
         Q.   Could it also be that exposure of a different kind might
     9        also have that effect?
              A.  Yes.  We believe, for example, that certain substances
    10        are actual inhibitors.  For example, selenium has been
              proposed as being an inhibitor; vitamin C has been
         proposed as being an inhibitor; so exposure to certain
              things may, in fact, reverse the process.  Once we have
    12        gone through the stage of promotion, we then get to the
              stage of progression.  This is the stage at  which you can
    13        actually detect some genetic abnormality within the cell.
 
    14        This change which takes place then enables the cell to
              either adopt a malignant potential, unlimited growth
    15        ability to divide, infiltrate surrounding tissues and
              possibly in the form of cancer spread to other parts of
    16        the body.  We know that all of this process may take many,
              many years to develop.  For example, even after the atomic
    17        bomb explosion at Hiroshimo people were developing
              malignancies many years after the initial exposure to the
    18        radiation.  So, even though people got a substantial
              exposure to radiation at that particular time, the tumours
    19        themselves did not develop until sometimes many years
              later; it could be as many as 20 or 30 years later, so it
    20        is a long process.
 
    Q.   Is there a term by which you describe the stage at which
              the condition may be said to be malignant?
    22        A.  There are certain defined characteristics which
              determine malignancy.  These are that there is invasion of
    23        surrounding tissues and/or the ability to metastasise, as
              we say.  What this means is that the tumour cells can
    24        escape from the primary site and spread either in the
              lymph system or in the blood stream to other parts of the
    25        body, where they then set up secondary cancers.
  
    26   Q.   I would like to go back, if I may, to the beginning, which 
              is how these things, if I may call them, are caused, what 
    27        I think you call aetiology.  Are there aetiological
              difficulties in the study of cancer?
    28        A.  There are.  One of the problems is that a lot of the
              direction of research is often stimulated by
    29        epidemiological studies which are in themselves purely
              observational, and they rarely can accurately specify a
    30        cause and effect relationship.  What they do, of course,
              is stimulate us to carry out research to see if we can