@j-brad The best thing you can probably do is try to cope with the feelings and stay on point with your vet. I believe that the test results will give you a clearer idea of your options as some cancers respond better than others. The vet will probably give you better advice than I can. I lost my first to cancer at 11, my second at 12, so at 10ish it is not surprising to see some problems.
Much would depend on the dog if it were me in the situation, I would consider is the dog strong and otherwise healthy, what is the cost, what is the probable outcome, what would the dog’s attitude be towards Chemo etc, you know your dog well, try to dig deep and thing as rationally as possible.
Having said all that, I have lost two and know just how deep it hurts to lose them, so I do appreciate how hard it is.
My first had a massive abdominal cancer, so was not realistically an option for chemo, plus he had other problems and was in pain from it, so euthanasia was the only choice.
My second had a cancer growth removed but never really came out of the anesthetic because she had a liver problem and seizures. I had already ruled out any major operations or chemo before that because of those, frankly if I could turn back the clock I would have just left it alone as trying to help just hastened her death.
In the right set of circumstances with an otherwise happy and healthy resilient dog, I would consider chemo if the vet recommends it or believes the prognosis to be good.
Good luck and fingers crossed.