As we discover more about the ways bone cancer gets started and grows, we get better at treating it. Osteosarcoma occurs most commonly in large-breed dogs age 7 years or older, say veterinarians at the University of Illinois College of Veterinary Medicine at Urbana. Osteosarcoma may be associated with a previously healed fracture site or internal fracture fixation devices, suggesting a link between chronic irritation and the start of malignant cell growth. In most cases, no known trauma has occurred. It is thought that microscopic traumas might occur in the growing parts of dogs' bones while the dogs are young, fast-growing, and active.
Veterinarians say that occasional lameness is common in the early stages of disease.
As the disease progresses, swelling and lameness become more obvious and more constant. The limbs are quite painful and may fracture spontaneously because the bone structure is very weak. A diagnosis of osteosarcoma is based on clinical signs, a characteristic radiographic appearance of the bone, and a biopsy that shows cancerous bone cells. A fluid sample from the bone marrow cavity taken using a very fine needle can also help in the diagnosis of osteosarcoma. Seventy-five percent of osteosarcomas occur in the long bones of the skeleton, the limbs.