It makes sense that the higher the rate of cell division, the higher the chances of mistakes to arise whether they are just ''bad luck'' mistakes or affected by extrinsic factors. Mutations are random but the underlying trigger may still be environmental. Of course, it is also true that even if you live in the perfect environment and are perfectly healthy, DNA mistakes will still happen inside your body and you may still get cancer. It's just a game of chances. You smoke, then your chances of a random cancer causing mutation increase. You eat healthy, exercise etc then those chances decrease, but they will always be there.