This is from some research at Colorado State:
http://web.archive.org/web/200106022.../nutrition.htm
Basically saying that a diet low in carbohydrates and high in fats & proteins may well make a difference.
There's another Colorado State (the vet school) study indicating that a high carb (grain) diet is perhaps implicated in
causing cancer, but I cannot find that article, the Co state site seems to be down.
Hopefully MaryDVM will chime in.
Oh - there's a lot of info here too:
http://www.bowchow.com/specific.html