Hi, I'm so sorry you are going through this with your baby, and are facing having to make the heart wrenching decision of when is the right time to let him go. When my Jack Russell Oreo who was 14 years old, was diagnosed with cancer, we faced those decisions too. My son didn't want to let her go, and after talking to my vet, she said it would come down to her quality of life, and if she was in pain. She said she could live with cancer just like people can, and you can manage symptoms with medications. She was still eating, pooping, she didn't play as much, she slept more than she had before, but loved her cuddles and love. In the end she passed away in her sleep at home, and we didn't have to make the decision to put her down. I was very close to making that decision, because she couldn't walk down the stairs of the front door anymore to go potty, and she started to have accidents in the house. The vet said these were signs that her quality of life was no longer good. If she couldn't go for walks, or play, slept all day, had accidents, and could not potty outside anymore, then she wasn't enjoying her life as a dog. It is the hardest decision you'll have to make, and is heart breaking, but we are the only ones who can make this decision for them, and they count on us to do this for them. My thoughts and prayers are with you and your family, and I hope you are able to find a way with your vet to keep her comfortable until you have to make a decision.