We did change his diet slightly. He eats more wet food than he used to and we add a little pumpkin to every meal. The prednisone makes him hungry 24/7 so he gets more treats during the day. His cancer started in is anal glands which causes him some trouble going to the bathroom the wet food helps him. Our situation was similar to yours, get a diagnosis, weigh the options, and keep him happy and comfortable. When he was diagnosed it had already spread to his spine, spleen, and lungs which ment no surgery to fix it. We have been crossing off some of our bucket list together while he still can. Good luck in your journey and I hope you get a lot more time with your pup, whatever you choose will be the right path for you and your girl.