I am so sorry to hear this. My wife and I lost our oldest cat to the very same thing last January at 11 years old.

We had it removed in summer of 2021 when we discovered a small lump, and it just ended coming back incredibly rapidly. We gave her all the love we could with the time we had left once we realized there was nothing we could do. Once the tumor abscessed and got infected, we had to put her to sleep in a matter of days.