Osteosarcoma is the most common bone tumor of dogs, affecting upwards of 10,000 animals every year. The appendicular skeleton (fore and rear legs) is the most common site, and the disease rapidly spreads to the lungs, as well as other soft tissue sites and bones. A diagnosis of osteosarcoma is made based on typical radiographic (x-ray) findings of the affected bone, and either fine needle aspirate or biopsy of the abnormal tissue. Treatment with surgery (typically amputation) alone is associated with rapid onset of lung metastases and a survival of 4 to 6 months. With surgery (most often amputation) and chemotherapy, survival is extended to 10-12 month post-diagnosis. While approximately 12,000 dogs are diagnosed with osteosarcoma every year, it is far less common in people. Unfortunately, the disease in people is as aggressive as in dogs and treatment with chemotherapy, while helpful in prolonging survival, can have devastating side effects. The CCOGC is interested in this tumor not only because it is uniformly fatal in affected dogs, but because studies by Khanna et al have shown that there is strong similarity between canine and human osteosarcoma based on global gene expression. It is our hope that studies through the CCOGC will help dogs and people with osteosarcoma.