
Very sadly yes I have had one of my Bassets, the last of my homebreds actually, who had oral cancer. The tumour was only discovered during a delayed dental - delayed because I'd spent 12 months fighting for the life of his sister, which wasn't to be. It was right at the back of his mouth, on the gum not the 'lip', to one side and my then vet removed it, with, he'd hoped, wide enough margins. It didn't come back there but quite soon afterwards, he developed another, same side, further forward which was much more aggressive. That final morning, I'd taken him into that vet again but it was bleeding badly and the lad wasn't good at all (he was in his teens) and after much discussion, we made the decision not to try operating but to let him go.
Those were a couple really bad years, losing the two last of my bloodline within those years. It's the possibility that can always happen when you keep two from a litter.
If your vet opts to remove the growth, I hope that's an end to it.