Well, we may not have Cancer Kitty after all. The biopsy came back negative - no sign of any cancerous growth. The vet is stumped why there might be a large, firm, painless lump on her leg, growing in size, that isn't some kind of tumor. It's definitely not an abscess. The current theory is scar tissue? Either that or some kind of error or weirdness in the biopsy.
So it's either:
1) wait and see
2) surgically remove the whole damn thing and send that all in for another biopsy
Poor kitty. She did manage to get the cone off once (but I was right by) and I let her have a grooming session as long as she didn't lick her hind leg. She was fairly rabid about getting her feet washed. I think she rustles about sometimes at 4 am just to get back at us for making her wear it.