Wouldn't dwarfs have less cancer simply because they have fewer cells that can become cancerous?
Also, on a related note, there's Peto's Paradox about why cancer rates are similar across species despite vastly different sizes (mice, humans, whales).
http://blogs.discovermagazine.com/loom/2011/02/28/the-mere-e...
Paper behind paywall: http://www.sciencedirect.com/science/article/pii/S0169534711...