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

Prev Next Index