Slate star codex kind of speculates [1] that it might have something to do with scale, ie -- in order to keep growing in a creature that large, the cancer cells need to coordinate among themselves and specialize to a degree that is not needed at smaller scale. In other words, before the cancer can grow large enough to threaten the host, "the cancer gets cancer."
Speculation by a psychiatrist of course, and mostly in service to a metaphor about some totally other topic, but I wonder if there's something to the theory.
[1] http://slatestarcodex.com/2014/06/14/living-by-the-sword/
Speculation by a psychiatrist of course, and mostly in service to a metaphor about some totally other topic, but I wonder if there's something to the theory.