Osteosarcoma, chondrosarcoma, fibrosarcoma and hemangiosarcoma all are malignant bone cancers. Osteosarcoma is the most prevalent bone tumor to affect dogs, accounting for roughly 85 percent of canine bone cancer diagnoses. Osteosarcoma is highly invasive, and by the time most dogs are diagnosed, the cancer already has metastasized, or spread, to other areas of the body. Understanding the risk factors, disease progression, diagnostic process and treatment options will enable owners to give their canine companions the best possible outcome.
Risks for Incidence
The exact cause of osteosarcoma is unknown, and no preventive measures can be taken to spare a dog from this dreaded cancer. Osteosarcoma has the highest incidence among large and giant-sized dogs. The tumors typically strike middle-aged and older dogs, and males are afflicted more frequently than females. Some studies also have linked a potential increase in risk for dogs that have sustained prior bone injuries. If your dog fits into any of these categories, be especially mindful of lameness or tenderness, and do not delay having him seen by a veterinarian at the first sign of discomfort.
Symptoms and Progression
Osteosarcoma is a primary bone cancer, meaning that it initially develops from within the affected bone. The tumor can strike any bone, including the ribs, mandible and spine, but the most common sites include the ulna and radius of the wrist, and the long limb bones, which include the femur, humerus and tibia. The first symptom that presents in osteosarcoma is lameness of the affected limb, which can come on suddenly or develop gradually. As the tumor develops, the affected area becomes more painful, and swelling becomes noticeable, resulting in a limp that escalates quickly from intermittent to constant. The dog may appear lethargic and show a decrease in appetite. The tumor grows rapidly, and as cancerous cells destroy healthy bone cells, the bone becomes brittle and is more susceptible to fractures. As the disease progresses, metastasis to the lungs, lymph nodes and abdominal organs occurs.
Diagnosis and Staging
If the symptomatic care prescribed by your veterinarian does not resolve your dog’s limp within a few days, then further diagnostic testing will be necessary to determine if the limp is caused by osteosarcoma. Radiographs of the painful area usually are enough to reach a diagnosis of a bone tumor, and a biopsy of the tumor is a painful procedure that typically is not recommended. Additional diagnostic imaging of the chest will reveal the presence of metastasis in the lungs, and collecting cell samples from enlarged lymph nodes also will confirm metastasis. Only 10 percent of dogs with osteosarcoma will have observable evidence of cancer spread, but the remaining 90-percent likely already will have microscopic metastases. A complete chemistry profile, blood cell count and urinalysis will evaluate the dog’s overall health. The results of all of these tests will stage, or define, the current status of the cancer, and determine which treatment options may be employed to pursue a favorable outcome.
Treatment and Prognosis
Due to the aggressive nature and extreme pain of osteosarcoma, amputation of the affected limb usually is recommended. Owners dread the notion of amputating one of their faithful friend’s limbs, but it is crucial to remember that dogs do exceptionally well with three limbs, and osteosarcoma causes painful suffering. Chemotherapy also is recommended to address the metastasis that already is occurring on a microscopic level. The combination of amputation and chemotherapy provides the best outlook for dogs with osteosarcoma, with half of the patients surviving for one year and a quarter of them surviving for two years. In a few cases, dogs who undergo this treatment plan will be cured. Dogs that do not undergo amputation and chemotherapy will die within an average six-month time span.