Katie is a youngish cat who we took in a few weeks ago and took up for investigation at the University Vet School because the vet we use at the kennels found a very large lump in her abdomen when checking her fitness to be spayed. The most common reason for this in a cat would be lymphoma, which is an invasive cancer with very bad prospects.
However, the Vet School did an exploratory operation on her tum on Monday and the "lump" seems to have been a very large internal abscess, which they've removed surgically. They're doing culture of the pus to check which antibiotics are best to use, but say provided the wound doesn't break down (some danger of this because it was actually attached to her gut wall) she's got a good chance of full recovery. They waited until today to phone me in case she went downhill after the op.