I found this info on a boxer forum when I googled your question:
www.boxerforums.com/post348768.html
It sounds to me like canine viral papilloma. It usually starts with one around the mouth then over time (one or two weeks), There will seem to be more. Some even get large and look like cauliflowers
They can be on the lips, gums, chin, the roof of the mouth, the back of the throat, even inside the mouth.
Generally even when biopsy's are done they are not cancerous growths.
With viral papilloma, even though they look bad they will grow & get/look worse for about 30 days from the onset and then go away in another 30 days. That is why 2 months is given as a general rule for them to go away (with no treatment at all).
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Hanna had a couple earlier this year. White, hard, grew up and out. Took her to the vet and that is what they said. Said it will heal on her own once immune system builds up, and common in pups. I then researched it further and started to supplement with echinacea. Then talked to a breeder who does alot of holstic practice. I then was told to try pepermint oil on the wart. I did that, and it went away in 2-3 weeks. The vet said it could take months.