We've been treating Thalia for a complicated vaginal infection/swelling/weird thing for about two weeks now. The first week it mostly looked infected, so we went with antibiotics and antiseptic rinse and cream and hoped that would clear it up. The next week, it was much less infected, but had suddenly ballooned up and... protruded, in a very disturbing sort of way. Still unclear on what it was (tumor? abscess? tissue reacting strangely to some problem farther inside?), the vet decided the best thing to do was remove as much as possible and send it off to be tested, so we did that. Those results got back today; unfortunately, it's not anything treatable like an abscess, but is instead a big fat nasty sort of tumor, very aggressive and tending to spread.
About all we can do now is keep her comfortable, so we'll do that.
Rats don't ever live long, but I sure wasn't expecting Thalia to be the next one off the ship.