My darling Timber was diagnosed and died the very same day with a lung tumour.
He was fine and then one day he woke up and wheezing a little. But he ate his breakfast as usual and I went off to work My son called me about 2 p.m. to say that Timer was really having trouble breathing. I left work and had him at the vet with 45 minutes. Xray's showed lung tumour, complicated by fluid in the lungs which need to be cleared immediately. He was put on diuretics and I brought him home. 30 minutes later, it was clear that he was in severe distress. My son and I put him in the car and drove the 10 minutes to emerg. He did not make it.
He was 12 years old.
In hindsight, I think it was the greatest kindness that he was diagnosed and died the same day. Had he not, I would have been agonizing over whether to treat him, or given his age, let him die quietly or put him to sleep. I did not have to face that choice.
But had he survived that day, I can say that I would not have put him through any more treatment. When I was sure that the pain of living was beyond, I would have sent him to the bridge.
Hugs to you! It's so hard to decide what is right for you and your dog. You can only take it one day at a time.
Take care.