[crusso]

Well, preventing Cancer has been a priority for evolution since the first multicellular organisms arose

It's only a "priority for evolution" to prevent cancer before the better years for breeding have passed - and evolution has done a fairly good job with that. After breeding and a little time for rearing young in the higher life forms, evolution has no real use for us.

[bayesianhorse]

Multicellular organisms have to control the replication and renewal of their cells constantly. In a simplified view, cancer is a loss of that control.