Bones are made of several different cell types, including cartilage, blood cells, fat, fibrous connective tissue and the calcium-depositing bone cells (osteoblasts). Any of these cell types are capable of developing into a tumor. Why do normal bone cells start to grow out of control and produce a bone tumor? At this time we don't know the answer to that question. What we do know is that almost all bone tumors are malignant (cancer), that is they grow the potential to spread into adjacent tissue and throughout the body. The most common malignant tumor of bone is the osteosarcoma, arising from osteoblasts. In dogs almost 10,000 new cases of osteosarcoma are diagnosed every year in the USA alone, with the majority of dogs being large and giant breeds. This tumor also occurs in people and cats, but is far more common in the dog.
Osteosarcomas will spread to other areas of the body, especially the lungs, very quickly. Usually by the time the dogs start showing signs of having the tumor (limping, bone pain, and swelling), the tumor has already spread. However, in the majority of dogs, the spread to other areas is initially microscopic so we cannot easily determine the extent of spread at the time of diagnosis. It is always adviseable though, to have a radiography (X-ray) of the chest taken before proceeding with treatment. The other bone tumors usually will not spread as quickly, but there can be great variation.
What form of treatment can be used for bone tumors? This depends greatly on what type of tumor we are dealing with. A biopsy must be taken in order to determine the tumor type. Once the tumor type has been identified, the correct form of therapy can be started. Chemotherapy, surgery and radiation therapy are the basis for the treatment of all bone tumors. The type of chemotherapy, the extent of surgery and whether or not radiation therapy is needed will be determined by the biopsy and evaluation by the oncologist. For most bone tumors, amputation of the affected limb has been the traditional form of surgical therapy. Metastasis (spread), however, remains a difficult problem in dogs undergoing amputation alone.
Recently, a variety of new anticancer drugs and surgical procedures have been developed that have resulted in improved survival and quality of life for dogs with bone tumors. All bone tumors are dangerous in the dog and should be treated as soon as possible. It is important to understand the seriousness of this problem and to work closely with your veterinarian.