So sorry to read this, Matt - the same thing happened to my previous dog - she was acting fine until one day she starting acting like she didn't feel good, and when I took her to the emergancy vet, it waas the same prognosis, massive tumors throughout. There really isn't any good reason to prolong a dog's life when the condition is that dire, other than to enrich some vet. It's much kinder to let them go with less suffering. But's it's always one of the hardest things any of us ever has to do - to let go of a dear friend when their time had come, as it will to all of us. - Bob B.