My Snickers was only five when she started limping and I absolutely believed that she couldn't possibly have bone cancer....fast forward to one course of Metacam and a persistant limp and then a positive x-ray after a clear one earlier...it did sink in. The important thing right now is to get a definitive diagnosis and then learn what you can and then see what you can do for Odie. Snickers was so young that I chose to amputate and give her chemo. She was doing reallly well but something -- probably a blood clot or possibly a brain tumor (more unusual) got her just before her fourth chemo. Nevertheless, I would still make the same decision now because of her age. I wanted to give her the best chance, and Snickers was so full of life and enthusiasm it didn't seem right to not do everything I could.
Join Circle of Grey and get their input and also try to consult with Dr. Cuoto's group at Ohio State University. Read and learn. Once the intitial shock wears off, try to make the best decision you can. My reasoning was that even if I had Snickers for another year, it was a good portion of her life and she was so full of enthusiasm for everything. Unfortunately luck ran out for us, but there are a lot of greys who have undergone the same and are doing well....the amputation actually helps alleviate the pain of bone cancer. Some survive beyond the one year as well....I think they can do a blood test to see if there is an elevated level of an enzyme that is a good prognosis indicator.
I'm very sorry you are dealing with such a lousy diagnosis, but there is hope. I wish you all the strength and the best for you and Odie. It is not an easy deciision and it really is hard when your dog is so young.
Sending hugs and wishing for the best for Odie.