You guys have to realize that in many cases we know certain things cause cancer. Not in everyone that uses them, this is a genetic issue, but in numbers vast enough to take the question pretty much out of the equation. Tobacco causes cancer. It s fact, not an guess, ditto second hand smoke. Millions of people have died because of it. We have essentially had the medical documentation since the 40's. If you engage in a known risk factor and you get a cancer.... the cause and effect issue is a mute point.

As to finite determination of a cause, in many cases there is. You find a cancerous cell and you find HPV16 in it, the mutation has characteristics that are unmistakable. This is only one example of many. If you do not believe this you should learn more about histology and etiology.

For sure there are some that we have no clue as to exactly where they come from, but that lack of understanding is not universally true to all cancers.