Re: Cancer Evolves - towards transmissiblity?
- From: Vend <vend82@xxxxxxxxxxx>
- Date: Sun, 27 Apr 2008 11:29:20 -0700 (PDT)
On 27 Apr, 12:21, Ernest Major <{$t...@xxxxxxxxxxxxxxxxx> wrote:
In message
<c92d864b-8cb7-43d2-8318-bf94460fb...@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
Vend <ven...@xxxxxxxxxxx> writes
On 26 Apr, 18:04, Jeffrey Turner <jtur...@xxxxxxxxxxxx> wrote:
<snip>
My uneducated guess is that transmissible cancers exploit the
mechanism used by the embryo to avoid destruction by the mother's
immune system. Is it possible?
There is also the question of why transmissible cancers appear to be
rare. In fact, the only two known examples, as far as I know, are the
two mentioned.
In both of them, the infection involves males, female-to-female
infection seems unlikely. Could it be that the mechanism to avoid
immune reaction towards the embryo stays turned off in males of most
species and for some reasons it's turned on in dogs and Tasmanian
devils?
A transmissible cancer requires two properties.
1) It has to be able to be transmitted from one individual to another.
2) It has to be able to overcome, at least temporarily, the immune
system of the second individual.
The first constraint eliminates the great majority of cancers in the
first place. Skin cancers are the only ones that have much opportunity.
(In principle a leukaemia could be transmitted by blood transfusions.)
Cancers of the respiratory and digestive system should in principle
have the opportunity of transmission, like parasites do.
In the original individual the immune system is constrained by the need
to attack non-cancerous self tissues. In a second individual this
constraint is lacking, so we can expect the immune system to be more
effective in dealing with non-self cancers. (For this reason cancer
research uses immune-compromised mice.)
In Canine Venereal Sarcoma the infection is usually transient - the
cancer is usually overcome, but it takes long enough that the cancer can
be transmitted to additional individuals in the interim.
In Devil Facial Tumour Disease I've seen it suggested that the
vulnerability of the species is due to inbreeding - the tumour is not
easily enough recognised as non-self.
--
alias Ernest Major
.
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- Cancer Evolves - towards transmissiblity?
- From: Jeffrey Turner
- Re: Cancer Evolves - towards transmissiblity?
- From: Vend
- Re: Cancer Evolves - towards transmissiblity?
- From: Ernest Major
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