My dog has the same thing...It doesn't bother her either, but I took her in anyway. I had it tested and it is what they call mesenchymal proliferation they said it is some sort of cancer. It is locally aggressive, but is slow to spread throughout the body. If I have it removed it is sure to grow back. However, no one can tell me how fast. They just tell me that it will eventually make her lame and I will have to put her down...sorry for the bad news
