You actually are putting yourself at risk with every smoke you have.
It's true that cancer is a disease essentially caused by a fault of our biology (its almost inevitable you will get some form of it eventually, generally something else will get you first however), however it is possible to exacerbate that fault, and to an extent cause it. Smoking, and more specifically the chemicals you take into your respiratory system from it, often causes the flaw of cell reproduction to be encouraged that causes cancer.
So, while you would almost certainly eventually get some form of cancer in life, assuming you lived long enough, smoking is simple increasing your chances of getting some specific types.
EDIT - And a lot of em ain't pretty.