I forget what tiny country it was but they did have an amazingly low cancer rate. It still was pretty unbelievable. The diet IS likely very healthy, though. It's mostly to do with the "healthy fats" and the fact that they have a lot of fresh veggies and a large variety, which means everything in moderation, like someone else said.
One of the key factors that's prevalent among all cancers are stressors for the individual. The stress levels of the average populace correlate directly with reported occurrences of cancer. I have a feeling that the stress levels of people on a small island living off of the local produce/whatever vary from the hectic, 9-5 world of places like the GTA. (i.e. http://www.stress.org/stress-and-cancer/)