Preventive is hard, primarily because there are many different cancerous conformations for a given organ.
All hope is not lost though, as there is a ton of very interesting anti-cancer drug therapies in late stage clinical trials. My girlfriend's father was actually cured of "terminal" late-stage liver cancer (caused by HepC -- wartime blood transfusion) a few years ago with an experimental drug cocktail. Even more interestingly, he was cured of HepC using another experimental biotech drug regimen simultaneously, which is still classified as an incurable disease.
It blows my mind that he was actually cured of two "impossible to cure" diseases simultaneously with advanced experimental biotech. That says to me that we are making some very serious headway. He volunteered to test both therapies because he had nothing to lose. He's been clean of both diseases for a few years now. Some day, the FDA may get around to approving them for general use.
Well mayber we finally making some progress then. I stand corrected.