I have to go along with Mr. Purcell on this one. We all "get" cancer. It has been shown time and again in labs that cells occasionally screw up. There is no organic machine that is perfect, even in the most pristine conditions. 

Otherwise, organisms would not have built-in mechanisms designed to "fight" and destroy cancerous cells.

The real issue, IMHO, is when a person (or animal) does or has something that interferes with this built-in immunity mechanism. This also explains why sometimes a baby will die of cancer... something is missing because of a genetic issue.