Bone Cancer In Dogs

My greyhound raced in Arizona but has live in BC with us for 5 almost 6 years. She has always had minor coughing and lameness due to what we thought was arthritis. In November of 2006 she was diagnosed with Osteosarcoma (bone cancer). OS tends to take dogs quickly and we opted for pain management only but now 9 months later she has a large tumor in her right leg and is sometimes completely lame and other times looks fine and runs full speed. She eats well and most of the time is a happy dog.
Someone has suggested this could be Valley Fever but is it possible almost 6 years later? Vets up here do not know of Vallet fever so i am trying to do research before bringing this possibility to them.