Sometimes these things do get infected and I'm thinking that the vet might prescribe antibiotics. Hannah had one on the hip that we we had *watched* for years and it started to get *bigger* quite rapidly. About 5 months ago, the vet finally agreed that it should be removed. She did real well through the surgery and recovery and now I can't even see a scar, although it looked horrible at first. It was NOT cancerous. So these things can sort out well even though things look ominous.