I've read that tumeric, and I think specifically the curcumin in tumeric, has been tested on labratory rats and had been shown to prevent tumor growth or reduce tumor size, and also reduces inflammation, if I'm remembering correctly. It is best to find one that is a standardized extract and has black pepper mixed in, because that helps increase the bioavailability of the compounds, otherwise it is not completely absorbed by the body and therefore is not as effective.
I have also read that cycling it (as in 2 weeks on, 1 week off) may be more effective than continuous use.
As far as getting them to eat it though...