Cat, tumor and Metacam

My cat had nose breathing issues for years and after xrays, CT and biopsy they found some tumor in the area "behind" the nose.

Cat is doing relatively fine, loud breathing aside and occasional cough-like episodes and we are doing our best to help him.

The oncologist who saw the results told us to give him 0,5 mg of Metacam every day for the rest of his life, since it has also a bit of a anti tumor effect and it helps with inflammation.

I trust a doctor but I can't help but thinking how a daily dose of anti-inflammatory does not sound great, first because as far as I know the body get used to it and second, I'm worried about his kidneys.

Anyone has anything to share about this?

Thank you