Hello,
I just found your question. Have you found a solution for your cat yet?
We had a cat at our shelter, that was found with an infected mass inside their ear canal. The mass was removed, but it wouldn’t get better. It was smelling bad and pus could be seen. When the mass started growing back, his whole ear canal was removed.
Maybe that is an option for your cat, too? It helped Tony a lot. No more itchy, smelling, hurting ear. Altough he had to war a cone during healing, but after that he was the happiest cat.
I wish the ebst for your cat.
Honestly, I’d be looking for a veterinary oncologist in your position.