My cat has a small sore on his upper lip. Behaviour/every everything else is fine. He's 2yrs old. Vet said it's most likely a rodent ulcer. They said a skin biopsy would be best - £500 but that would only rule out it being something else, like a fungal infection. If it is an allergic reaction, which they suspect it is, it won't tell them the cause. The other option is to try out steroid injections which they didn't give me a price for but may help if it is an allergy. What does everyone think? I'm just not sure £500 is worth it when I suspect it's just going to tell us that it is in fact an allergy.