Osteosarcoma is a form of bone cancer that tends to be most commonly diagnosed in middle aged to senior dogs. Any breed can develop osteosarcoma but the larger heavier boned breeds tend to be the most prone to the condition. The breeds most often associated with the condition include the giant and large breeds such as the Great Dane, Newfoundland, St. Bernard, Irish Wolfhound, Rottweiler, Labrador, Golden Retriever, Boxer and Weimaranar. The group of dogs that weigh over 80 pounds are the most commonly affected, with this weight range 60% are more likely to develop the cancer than any lighter breeds of dogs. Males of any breed are more commonly diagnosed with the condition than females, perhaps because the bones tend to be heavier and more developed in males of most breeds.

The causes of osteosarcoma are not clearly understood but there are several theories. Two of the most likely theories include the rapid growth of the bones and the increasing stress on the growth plates in larger dogs may contribute to injury of the long bones, resulting in a weakening of the joints and an increased likelihood of cancer. The other theory, which is closely related indicates that stress, trauma and fractures in early life when bones are growing may contribute to cell irregularity in the bones, later resulting in the development of cancerous cells.

The osteosarcoma is typically diagnosed through x-rays when the owner brings a large or giant breed of dog in with a complaint of lameness. Often this lameness has seemed to come and go and has been present for months before the vet is consulted. Usually the joint, typically the knee, will seem swollen, but it will be a hard swelling of the bone, not a fluid build up. X-rays then confirm that the growth or swelling is around the growth plate, which is a good indication to the vet that the dog has osteosarcoma. Any limb can be affected, and dogs may have more than one limb affected at any time. Usually by the time the condition is diagnosed, the tumor will have metastasized to the lungs, so typically dogs with osteosarcoma are also treated with chemotherapy after a chest x-ray is completed, even if no additional tumors are noted in the lungs. It is estimated that at least 90% of all dogs diagnosed with osteosarcoma will also develop some form of cancerous tumor in the lungs. There are, however, other conditions that can cause a swelling or bulge at the growth plate on a bone so to confirm the diagnosis a biopsy will be completed.

Unfortunately the only way to treat osteosarcoma is to remove the affected limb since the complete joint is involved. In many cases this can be successful, however the quality of life for the dog needs to be considered depending on the age of the dog, location of the amputation and possible spread of the cancer before diagnosis. After the surgical process chemotherapy will also be necessary to ensure there is no further concerns regarding the cancer. Dogs that develop osteosarcoma should be reported to the breeder, as there is likely a strong genetic link to this horrible condition.