Riley is a 12 1/2 year old German Shorthair Pointer. She had been having trouble with her knee as far back as August 2016, but x-rays didn’t reveal anything, and it just sort of went away. She was back at the vet in late January, and there was massive swelling in the knee – so much that it was dislocating. We took her to a specialist, and they pulled 25ccs of fluid out of the joint. Lab tests showed nothing except severe swelling.
At this point, we opted for exploratory surgery, with a possible kneecap repair if needed. The surgeon found “lots and lots” of nodules in the leg, but nothing wrong with the kneecap or Riley’s ACL. Lab tests on all fifteen biopsies came back showing no cancer. We were elated, if baffled. A course of antifungal meds (just in case it was valley fever, also she tested negative for that, too), did nothing. We were back to square one. We had some of the slides sent to CSU, and the diagnosis came back with synovial sarcoma/histiocytic sarcoma. Without amputation, the prognosis is very poor. So, Riley is scheduled for amputation in a couple of days. Gulp. 
Hi I just came across this site… I also have a german short hair pointer named Cole. He is 8 years old was recently diagnosed with an osteosarcoma. We are going in for amputation early tomorrow morning. I am just sick and nervous and sad. I know he will be ok, as you know their breed is resilient and strong and love to have fun… I think this whole thing is worse on us humans. I hope everything goes well for you and your girl.
Fingers crossed for you and Cole. I’ll be thinking of you.