Buddy, my 12 year old mixed breed male dog, developed a sore on top of his right paw. After treating it with various things, I noticed it isn't just on top, but actually about the size of a small button under the skin. I can put my fingers under it and lift it up! Well, it is not healing, but the top part that shows has become black and hard. He keeps biting and licking it. I know the Vet is my next option if nothing else makes it go away. I fear it may be a cancer. Please help!