I lost a cat to breast cancer at the beginning of 2024 and a kitten to brain cancer in 2020. The kitten absolutely killed me, because I spent so much money and went through so many different diagnoses that offered varying levels of hope for improvement. He literally passed while he was on the vet's table to be put down, and the only reason I ever found out what happened is that my vet has been a family friend for decades and was bothered enough by it to do an autopsy.
The comforting thought I always have is that our pets have far better lives in our care than they would've had. Most of my cats have lived into their late teen years. They've been warm and known no need unfulfilled. They're the lucky few compared to ferals and strays. A cat who knows what brushes are and can openers sound like is probably a very fortunate pet indeed.