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Did your vet do a fungassy to rule out ringworm?
I have another question, and then I'll get your answer done.
Has your vet treated this with anything yet?
Okay, thanks for your quick reply. Ringworm can cause crustiness and scaling so I would recommend testing for it to be certain because of the circular shape of these lesions. It probably isn't ringworm, but I think it should be ruled out. Here is a link to a page about it:
I think your vet is right that a biopsy should be done if it isn't ringworm. It could be cancerous, or it could be something else entirely such as an allergic reaction, inflammation, or infection. There's no way to know for sure without doing a biopsy. Here is a link to a page with a chart of different conditions in cats causing growths:
If you have further questions let me know. If this answer is helpful please click accept. Thank you.