Here's to his continued comfort, whatever time period that may be. I agree, quality over quantity.
I had to put my 7 year old Doberman down when his prostate cancer was no longer manageable. My vet was awesome. She was very straight forward and did tell me that yes, they could treat for cancer, and no, it wouldn't work. Said she had to put her own dog down for the same reason.
Take heart. Every dog is different. Andy, the best golden in the world (sorry, Triumph, you are second) lived 16 years. Sure, the last few he moved like a Chinese dragon, but he was a happy dog. He lived his best life. So shall Triumph.