Daisy had something very similar that we just had removed & are awaiting the pathologists report. I had Googled "mast cell tumor" and was sure that was what she had. On the initial exam at the vet's, the vet aspirated it & did a microscopic exam, which showed that it was not mast cell. The vet was not surprised, as there are so many other things that it could be. My Google search didn't show "all the other things", so I was being narrow minded about it.