Cancer, I'm sure. There's no way that the fumes are not carcinogenic.
A bigger concern, though, is the fact that at least 75% of the guys I see at the track are chain smokers. Intentionally inhaling smoke will kill you long before the smoke that comes out of a nitro engine's exhaust.
I don't understand. It's not logical at all. If you quit smoking cigarettes, you could probably pay for your hobby each year.