Isabella had one right on the middle of her back. It started out the size of a pea, so the vet said leave it. They said it would probably shrink on its own. Well needless to say it got to be about the size of a fifty-cent piece. It looked like it was finally "healing" so the vet said "no worries". It had by this time, got crusty, like a large scab. But they said it would be okay. Well right in the middle of our vacation she was wet from swimming (which the vet said was fine) and the top of it came off and she had a really deep hole in her skin and it was infected and pusy. This all happened within 7 days of her first vet appointment. It grew really fast. So I ended up driving her all the way back home to our vet and they removed it that day. She is fine now, just has a 2 inch scar on her back. By in my experience, DON'T EVER WAIT. Had we insisted they remove it when it was small, she would not have a huge black scar or had that awful infection.