Osteosarcoma (OSA) is the most common cancer originating in the bone in dogs. Current treatments for OSA range from quality of life focused care, such as pain management, to amputation and chemotherapy. Unfortunately, regardless of the path pursued, very few dogs are cured of this cancer. Quality and quantity of life are limited in patients with OSA due to significant destruction of normal bone, which puts patients at risk of fractures. Furthermore, OSA has a high rate of spread to other areas of the body (metastasis), most commonly to the lungs. The investigators recently identified abnormal activation of a protein transcription factor called NF-kappaB in both patient-derived tumor samples and in established OSA cell lines, and believe the increased activity of this pathway may be contributing to some of the aggressive characteristics of OSA in dogs. Recent information indicates that a drug called bortezomib may be able to limit or completely stop the activation of this protein. Bortezomib has recently been investigated in multiple cancer types in humans with some encouraging results. This study will investigate the role of NF-kappaB and bortezomib in canine OSA.