Re: Does Size Matter? -Reply

[Charles Willis <CAW@nrc.gov>]

Martin,

I believe you are over-simplifying when you assume that the probability of
radiogenic cancer is simply proportional to the number radiation-produced DNA
breaks.  The number of DNA breaks caused by radiation always is quite small
compared to the number of DNA breaks from other causes and the repair process
is of overwhelming importance.  We do not know how radiation affects
carcinogenesis, but we do know that some cells are more radiosensitive than
others.  Biology is inherent complex and our models necessarily are gross
simplifications.

If  the number of DNA breaks were the critical parameter, the cancer rate of the
US population would have increased with the increase in average weight because
body temperature such have remained essentially constant.  This has not
happened.  Smoking and lung cancer seem to dominate the changes in age-adjusted
cancer rates in the US (and probably elsewhere).  Apart from lung cancer, the age
adjusted cancer mortality rate in the US generally has declined as the average
weight increased since WW-2.  Thus it is not surprising that the American Cancer
Society's summary of cancer data does not list obesity as a risk factor for the
principal cancers in the US.

Charlie Willis
caw@nrc.gov
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