It's always a sad day when it's time for your trusted buddy best friend to leave this earth. My condolences to you and your wife. I rescued a boarder collie mix about a year and a half ago and 6 months later noticed she was limping badly on one rear leg. After seeing several vets it was finally diagnosed as bone cancer. Last November I had her left hind leg amputated so she didn't have to suffer the pain and so far she's doing quite well. Every time we take walks I am looking for signs of the cancer spreading but still hoping she's one of the low percentage who actually get a cure by the procedure. Hoping the day death become necessary is far in the future.
Good luck / Skip