[ RadSafe ] Are rodents good models for studing radiaton-induced cancers?

[John Jacobus]

I saw this article and thought that it raises some
intriguing questions.
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Nature Reviews Cancer 5, 807-819 (2005)/nrc1715 
  
CANCER IN RODENTS: DOES IT TELL US ABOUT CANCER IN
HUMANS?  

Vladimir N. Anisimov, Svetlana V. Ukraintseva &
Anatoly I. Yashin

Abstract

Information obtained from animal models (mostly mice
and rats) has contributed substantially to the
development of treatments for human cancers. However,
important interspecies differences have to be taken
into account when considering the mechanisms of cancer
development and extrapolating the results from mice to
humans. Comparative studies of cancer in humans and
animal models mostly focus on genetic factors. This
review discusses the bio-epidemiological aspects of
cancer manifestation in humans and rodents that have
been underrepresented in the literature.

Summary

--Whereas laboratory rodents (namely mice and rats)
are similar to humans in some aspects, there are
important differences among mammalian species that
make valid interpretation and extrapolation of the
results from rodent cancer experiments to humans
problematic.
--The five most common human cancers are those of the
breast (female), the prostate (male), and the lungs,
colon, and stomach (both sexes). Mammary tumours are
also common in rodents. However, there are no rat or
mouse strains that exhibit a high incidence of
spontaneous carcinomas of the stomach or colon.
--A decrease in the overall risk of cancer owing to
old age has been recorded in both human and rodent
studies. Three important factors could be responsible
for this intriguing decline: detection bias,
differential selection, and the effects of individual
ageing. Studies in rodents argue against a diagnostic
bias as a leading cause.
--The risk of cancer has increased over time in most
human populations. Why this is remains unclear, but
addressing this problem is crucial for understanding
the nature of cancer.
--Some studies indicate that the differences in cancer
incidence rates between males and females are similar
in rodents and humans. This is a surprising finding
that requires additional explanation.
--Whereas tumours often grow at a slower rate during
old age, the chances for survival of a transplanted
tumour in a recipient host often increases with rodent
age. This is in agreement with human data indicating
that ageing can both decelerate tumour growth and
increase the chances of latent tumour survival in
older organisms.
--The spontaneous regression of tumours is a rare
phenomenon in adult humans, whereas it is common in
mature laboratory rodents. This effect and its
implications need further investigation.
--Few rodent carcinogens were established as clearly
carcinogenic to humans. Similarly, some human
carcinogens are not carcinogenic to rodents. This
creates a significant problem for interpreting the
results of animal experiments with carcinogens in
relation to humans.
--These and other differences warn against the simple
extrapolation of the results of rodent experiments to
humans and call for further investigation of this
important problem to reliably predict cancer risks, as
well as foster success in treating human cancers based
on data from laboratory animal studies.


+++++++++++++++++++
>From an article about physicians doing clinical studies: 

"It was just before an early morning meeting, and I was really trying to get to the bagels, but I couldn't help overhearing a conversation between one of my statistical colleagues and a surgeon.

Statistician: "Oh, so you have already calculated the P value?"

Surgeon: "Yes, I used multinomial logistic regression."

Statistician: "Really? How did you come up with that?"

Surgeon: "Well, I tried each analysis on the SPSS drop-down menus, and that was the one that gave the smallest P value"."

-- John
John Jacobus, MS
Certified Health Physicist
e-mail:  crispy_bird at yahoo.com

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