Do sharks really not get cancer, and if not why?

[abcd]

Jim Barron wrote:

> I have read that there is an oil in shark liver that acts to chelate
> mercury.  Would this be Squalamine?   Since sharks are so high on the
> marine food chain and mercury is known to be  a problem in things like
> tuna, etc. presumeably they must have SOME method for dealing with it.
> 
> jdbarron at cphl.mindspring.com

Humans and mammals use a chelating protien called metallothionen, which
regularly transports metals in the blood but will also chelate heavy
metals.  Sharks might use something similar.