Abscess or something else?

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Hi everyone, I haven't posted here in a long time but i figured it would be the best place for some advice.

I've booked a vets visit, with a good hamster vet, but I just wanted to see if anyone else has had a hamster with anything similar.

Luna is a 20 month old female Syrian. She isn't showing many signs of ageing except her thinning hair. She doesn't sit still, eats everything given to her, loves to dig- still a very active and alert hamster.

I was cleaning her cage today so this meant handling her a bit, giving her a health check/once over, and I noticed a red bump on her back, to the left of her tail. It is not a scent gland, those are a bit further up. It looks almost like a big spot on her back- like maybe it could get popped? (I am not going to try anything like that of course). I haven't managed to get a picture because she's so wriggly and it's underneath her "skirt" but I will try later.

From the cage clean I could see she's eating and bathrooming normally. She's grooming normally in her sandpit, her coat looks well groomed without any hair pulled out or any kind of rash anywhere. She let me touch near the bump without any issue, and is currently rushing around hoarding up food and rearranging her cage to her liking (again making it hard to photograph). I weighed her and she hasn't lost anything (she's around 150g). I'm kind of hoping her normal behaviour, appetite and weight rule out this being something too sinister.

Has anyone else had any experience with something like this? Does anyone have a clear image of what an abscess looks like? Or any idea what else this could be?