It's a wart. Ugly but harmless. We had a doe killed on our lease a few years ago that had dozens of them. Called the Dept. of Wildlife & Fisheries. Biologist came out within hours. Said they were harmless and confined to skin only. We skinned her. Meat was fine.
http://www.michigan.gov/dnr/0,1607,7-153-10370_12150_12220-26637--,00.html