The only way to tell for sure a grey horse has skin cancer is to remove the hide (not real great for the horse). Grey horses are slaughtered at a seperate plant than colored horses because of the incidence of cancer so I would say the incidence must be pretty high. Very few horses ever show any signs of it and fewer still ever have to get treatment or put down because of it. It's not something that would factor in to my decision on rather to buy a horse or not.
There's nothing like the Rockies in the springtime... Nothing like the freedom in the air... And there ain't nothing better than draggin calves to the fire and there's nothing like the smell of burning hair. -Brenn Hill