This came up on a discussion list. Apparently some raw commercial diets have high levels of thyroid ground in and this may produce this rare -- and generally serious -- thyroid cancer in dogs. If you feed a raw commercial diet, it might be wise to check with the manufacturer on levels of thyroid included (and if they verify content):

I also see that someone noted that amongst dog cookbooks for those who home-prepare, the Whole Dog Journal had recommended The Healthy Dog Cookbook. If anyone has that issue, maybe let us know some of the others?