Osteosarcoma, commonly abbreviated as OSA, is a malignant tumor of osteoblasts, the cells that make bone. Osteosarcoma is the most common primary bone tumor in dogs. We do not know what causes canine osteosarcoma. There is no gender predilection, however, osteosarcoma is detected more often in large-giant breed dogs than small dogs. Trauma and radiation therapy have been implicated as contributing factors in some dogs. While osteosarcoma may develop in any bone, the majority of the dogs develop lesions in the long bones of the legs (appendicular locations). Classically, this tumor occurs near the knee (distal femur & proximal tibia) and away from the elbow (proximal humerus & distal radius).
What are the Signs of Osteosarcoma in Dogs?
Clinical signs associated with osteosarcoma include progressive lameness and a firm painful swelling of the affected bone. Weight loss, decreased appetite, and lethargy may also be present.
Recommended Diagnostic Tests
- Radiographs of the affected area – demonstrate important changes in the bone
- Thoracic (chest) radiographs – less than 20% of patients will have radiographic evidence of pulmonary metastasis at diagnosis, however most dogs have microscopic metastasis that cannot be seen on the radiographs
- Bloodwork and urinalysis – to determine the alkaline phosphatase level and look for the presence of concurrent diseases
- Bone biopsy/aspirate – may be discussed to confirm the tentative diagnosis prior to determining a treatment plan, however, a biopsy may exacerbate lameness or further weaken the bone and the results rarely impact treatment recommendations
- Osteosarcomas are very aggressive tumors – they are locally invasive and quickly metastasize (spread) to distant sites in the body. It has been proven that the vast majority of dogs have undetectable metastasis at the time of diagnosis. Therefore, the treatment of choice for a dog with osteosarcoma is a combination of local and systemic therapy.
Treatment Options for Osteosarcoma in Dogs
- Surgery – removal of the affected bone, most often requires amputation but in some cases a limb-salvage procedure may be an option
- Radiation therapy – used for pain control and to improve quality of life when surgery is not a viable alternative
- Chemotherapy – to manipulate tumor growth throughout the body but is most effective when the tumor burden is small
- Bisphosphonates (pamidronate) – to aid in bone remodeling, pain control and potentially exert anti-neoplastic effects
- Analgesic medications such as narcotics or opioids
- NSAIDs – in addition to pain control, NSAIDS may alter tumor progression via COX-2 inhibition
Prognosis for Dogs with Osteosarcoma
The longest survival times are achieved with the combination of surgical removal of the primary tumor and chemotherapy (median survival ~ 12 months) whereas local therapy alone (surgery or radiation therapy) +/- supportive care results in a median survival time of < 6 months.
- Tumor stage – dogs with detectable regional or distant metastasis at diagnosis have shorter survival times
- Serum alkaline phosphatase level – an elevated ALP level is associated with a more aggressive tumor and shorter survival time
- Tumor location – osteosarcomas associated with the axillary skeleton tend to metastasize more slowly and therefore, local therapy may result in longterm control