I am surprised that no one responded to this.....I guess I am the only one who has had cats with that lump of fatty tissue on the back!
I once ask the vet about it and was told it was nothing now I hear on the news they must have known this knowledge for a long time!
It's just that they are so common and harmless.
I have a dog with one on her chest, and I had one for a couple of years on an eyelid, where they seem to be common on people.
Sometimes they stay, sometimes the go, but almost always they are harmless.
SO9
The missus cat got something like that, but it wasn't after any vaccinations as the vet thought it might've been.
Seems "Tristan Cameron the Black" lept and landed funny.
He got what amounted to a massive bruise, which did this funny puff up and after it healed it did the fatty lump like thing.
Freaked us out.
It did go away.
But a fatty lump on the spine IS a cause for concern as it may pinch nerves.
Especially if it is close to where vaccinations are given.
(Sometimes is a skin reaction to vaccinations or so I'm told.)
I don't recall what can be done about it though.