Thank you for all your good thoughts, and many purrs and hugs. We are truly overwhelmed with all your well wishes.
Bubbles' blood work came back normal. Kidney function, red and white blood cell counts are also normal. It seems that the main problem is his breathing, and unfortunately if it is indeed cancer metastasized in his lungs there is not much to be done, despite the normal test results.
On Tuesday he will go for an ultrasound and a biopsy. This is the least invasive way to get a definite answer. If the current diagnosis is correct, there is not much point putting him through major surgery, so that is why I chose this option rather than immediate surgery.
Bubbles is doing reasonably well. He is eating, drinking, using the litterbox, etc. He is going up and down the stairs without trouble, but is a bit winded when he gets to the top. He spends most of his time dozing, but does not seem in pain (although it is difficult to know for sure). He seems more irritated with his breathing than anything else. Right now he and Squish are both sleeping on me as I lie on the sofa. Here is a picture.
You can also see Trouble's ears sticking out behind the sofa armrest. And that he has been playing with the blinds!
Once again thanks for all the support.