I can tell you that I have had two cats with lung cancer and that they both had obvious breathing problem within a few weeks of diagnosis, and they were diagnosed quite early for cats. They had noisy breathing soon moving to labored breathing, it's quite obvious. They never had the sniffles or any signs of a cold. You are very right, it's far, far too soon to say it's the end.

I understand your frustration very well. My step-mother doesn't take her cats to the vet very often, and says the same kind of thing "I know my cats, I can sense things". Well, yes, I sense things too but my cats are off to the vet at the first sign of a problem, and they keep going to the vet until they are either well or we can do no more.