The etiology of osteosarcoma is unknown. There has been speculation about a viral cause, but this has not been proven. There is also the possibility of a genetic cause involving the p53 gene and an Rb gene which normally act as tumor suppresser genes and for some reason are altered preventing their usual functioning. This too remains to be proven. Previous trauma has also been implicated.
Lameness is a common presenting symptom due to involvement of the long bones of the legs.
There may be swelling to the affected leg and the dog may appear to be in pain. There may also be a history of mild trauma just prior to the onset of lameness that causes one to suspect a more benign orthopedic injury. There may be a history of intermittent lameness that becomes progressively worse. If the ribs are affected, a palpable, painful mass may be present. Osteosarcomas tend to metastasize to the lungs, but respiratory distress may not develop for months.