I would say you can lessen your chances of cancer, but saying most cancers are preventable I would say is debatable.
Isn't preventing equivalent to lessening your chances?
It's the same with AIDS...you are lessening your chances by remaining monogomous, wearing condoms, not using shared needles. ...but you can still get the disease, despite those preventative measures.
With cancer, use sunscreen, don't smoke, get body scans yearly, check for lumps, etc. Sure, it can still pop up, but in most cases, it can be treated so it isn't fatal.