
We sadly had one with this. Diagnosed at 12. At the time, apart from the hard lumps I felt which took me to my vet, I'd not have known he was ill. After discussion, and even if dogs do tolerate Chemo better than humans, this still means vet trips which for some dogs, is enough stress without having cancer, we opted for no treatment. He had 6 months totally normal time with us after his diagnosis to the point I started to think the diagnosis was wrong! Not so - on his final day he just 'crashed'. Didn't come for his second meal with the others and I found him collapsed in the living room.
My neighbour had an elderly hound - 14+ - who she put through Chemo and afterwards said for the little 'extra' time he had, it wasn't worth subjecting him to the stress of vet visits. She said never again. We'd moved by the time this happened, so I didn't see first-hand how he was but for me, it would depend on the individual animal, his age, the prognosis with or without Chemo.