I talked to a second, more experienced, vet today. It looks like this tumor is a kind of cancer after all, just not what we normally think of because it doesn't travel through the blood and metastisize to other locations. (The lack of spreading is what the first vet meant by "benign," but that term wasn't clear to me.) So we will need to wait for her biopsy location to heal for 30 days and then do the extra surgery to get clear margins.

I asked about radiation: he said that compared to the surgery, radiation would cause Oreo more physical and mental stress and be less effective.

Thanks for listening, and I'll let you know how she does in a month.